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Satya Meka provides the Separate RGB effect plug-in on the After Effects Scripts website. This effect—which was written with Pixel Bender—offsets, scales, and rotates each color channel of an image separately.
Chris Forrester provides a video tutorial on his website that shows how to use the Channel Mixer, Shift Channels, and Set Matte effects to create mattes from color ID passes from 3D applications. The tutorial also provides an animation preset that sets up the parameters in the Channel Mixer effect for the use of an RGBCMY color ID pass.
The Arithmetic effect performs various simple mathematical operations on the red, green, and blue channels of an image.
This effect works with 8-bpc color.
Operator
The operation to perform between the value you specify for each channel and the existing value of that channel for each pixel in the image:
Clip Result Values
Prevents all functions from creating color values that exceed the valid range. If this option isn’t selected, some color values may wrap around.
The Blend effect blends two layers using one of five modes.
You can blend layers more easily and quickly using blending modes, but you can’t animate blending modes. The advantage of using the Blend effect is that you can animate it. (See Blending modes and layer styles.)
This effect works with 8-bpc and 16-bpc color.
Opomba:
To use a layer as a control layer for the Blend effect but not show the layer in the rest of the composition, deselect the control Video switch 
for the control layer. (See Layer switches and columns in the Timeline panel.)
Mode
Blending mode:
Color Only colorizes each pixel in the original image based on the color of each corresponding pixel in the secondary image.
Tint Only is similar to Color Only but tints pixels in the original image only if they’re already colored.
Darken Only darkens each pixel in the original image that is lighter than the corresponding pixel in the secondary image.
Lighten Only lightens each pixel in the original image that is darker than the corresponding pixel in the secondary image.
Crossfade causes the original image to fade out while the secondary image fades in.
Opomba:
You can create a crossfade without applying an effect by animating the Opacity property of one layer on top of another. However, this technique doesn’t work if the frontmost layer has any transparent portions (which allow the other layer to show through, even when at full opacity). The Crossfade mode creates a proper crossfade between two layers, even if both have transparent regions.
Blend With Original
The transparency of the effect. The result of the effect is blended with the original image, with the effect result composited on top. The higher you set this value, the less the effect affects the layer. For example, if you set this value to 100%, the effect has no visible result on the layer; if you set this value to 0%, the original image doesn’t show through.
If Layer Sizes Differ
Specifies how to position the control layer. The quality setting of the layer affects Blend only if Stretch To Fit is selected and if the layers are of different sizes. Stretching at Best quality is much smoother.
The Calculations effect combines channels of one layer with the channels of a second layer.
This effect works with 8-bpc and 16-bpc color.
Input Channel
The channel to extract and use as input to the blending operation. RGBA displays all channels normally. Gray converts all color channel values for a pixel to the luminance value of the original pixel. Red, Green, or Blue converts all color channel values for a pixel to the value of the selected color channel for the original pixel. Alpha converts all channels to the value of the alpha channel for the original pixel.
Invert Input
Inverts the layer (subtracts each channel value from 1.0) before the effect extracts the specified channel information.
Second Layer Opacity
The opacity of the second layer. Use a setting of 0% for the second layer to have no influence on the output.
Invert Second Layer
Inverts the second layer (subtracts each channel value from 1.0) before the effect extracts the specified channel information.
Stretch Second Layer To Fit
Stretches the second layer to the dimensions of the original layer before blending. Deselect to center the second layer on the original layer.
The Channel Combiner effect extracts, displays, and adjusts channel values for a layer. It is GPU-Accelerated for faster performance.
Opomba:
You can use this effect to view any channel as a grayscale image by choosing the channel from the From menu and choosing Lightness Only from the To menu.
From
Which values to use as input; the first several items in the menu are multichannel combinations of input and output options, so they don’t require you to set a To value.
Saturation Multiplied uses the saturation value multiplied by the lightness value, where lightness is the minimum distance to black or white. For example, a dark or light blue pixel has a lower value than a bright or pure blue pixel. This option represents the most common view of the saturation value of a pixel.
Min RGB uses the lowest value among the red, green, and blue channel values.
Max RGB uses the highest value among the red, green, and blue channel values.
To
The channels to which to apply the values. Choose Red Only, Green Only, and Blue Only to apply the value to one channel only and set the other color channels to zero. Choose Alpha Only to apply the value to the alpha channel and set the color channels to 1.0. When you select Hue Only, the applied hue value is combined with 50% lightness and 100% saturation. When you select Lightness Only, the applied lightness value is combined with 0% saturation, which then gives the hue no influence. When you select Saturation Only, the applied saturation values are combined with 0% hue and 50% lightness.
The Compound Arithmetic effect mathematically combines the layer to which it is applied with a control layer. The Compound Arithmetic effect is intended only to provide compatibility with projects created in earlier versions of After Effects that use the Compound Arithmetic effect. Using blending modes is usually more effective than using the Compound Arithmetic effect.
This effect works with 8-bpc color.
Stretch Second Source To Fit
Scales the second layer to match the size (width and height) of the current layer. If this option is deselected, the second layer is placed at the current size of its source, aligned with the upper left corner of the source layer.
Blend With Original
The transparency of the effect. The result of the effect is blended with the original image, with the effect result composited on top. The higher you set this value, the less the effect affects the layer. For example, if you set this value to 100%, the effect has no visible result on the layer; if you set this value to 0%, the original image doesn’t show through.
The Invert effect inverts the color information of an image. It is GPU-accelerated for faster performance.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
Channel
Which channel or channels to invert. Each group of items operates in a particular color space, inverting either the entire image in that color space or only a single channel.
Blend With Original
The transparency of the effect. The result of the effect is blended with the original image, with the effect result composited on top. The higher you set this value, the less the effect affects the layer. For example, if you set this value to 100%, the effect has no visible result on the layer; if you set this value to 0%, the original image doesn’t show through.
The Minimax effect assigns each channel of a pixel the minimum or maximum value for that channel found within a specified radius. It is GPU-Accelerated for faster performance.
This effect can be used to enlarge or reduce a matte. For example, a white solid area surrounded by black shrinks one pixel on each side using Minimum and a radius of 1.
The quality setting of the layer doesn’t affect Minimax.
This effect works with 8-bpc, 16-bpc color, and 32-bpc color.
Operation
Minimum assigns each channel of a pixel the minimum value for the specified channel within the specified radius. Maximum assigns each channel of a pixel the maximum value. Minimum Then Maximum performs the Minimum operation and then the Maximum operation. Maximum Then Minimum performs the Maximum operation and then the Minimum operation.
The Remove Color Matting effect removes color fringes (halos) from layers with premultiplied color channels. Halos often occur when an area of partial transparency retains the color of the original background and is composited into a context with a different background color. Use this effect along with effects that create transparency—such as keying effects—to achieve more control over the appearance of areas of partial transparency. (See Alpha channel interpretation: premultiplied or straight.)
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
Use Background Color to specify the new background color. To allow this effect to generate color values outside the range 0.0-1.0 when working in 32-bpc color, deselect Clip HDR Values.
The Remove Color Matting effect was previously known as the Unmultiply effect. The old name refers to the fact that this effect functions by unpremultiplying color channels—removing the result of the background color being premultiplied with the color channels of the layer in areas of partial transparency. This functionality differs from Knoll Unmult and other effects that synthesize an alpha channel from the color channels in an image.
Todd Kopriva provides a post on the Adobe website that describes the use of the Remove Color Matting and Shift Channels effects to remove black backgrounds from images.
The Set Channels effect copies channels from control layers (source layers) to the red, green, blue, and alpha channels of the effect layer. It is GPU-accelerated for faster performance. For example, you can take the luminance values of the pixels of a control layer and use them as the blue values for the pixels of the effect layer.
This effect works with 8-bpc, 16-bpc color, and 32-bpc color.
The Set Matte effect replaces the alpha channel (matte) of a layer with a channel from another layer above it for the creation of traveling matte results. It is GPU-accelerated for faster performance.
The Set Matte effect is intended only to provide compatibility with projects created in earlier versions of After Effects that use the Set Matte effect.
This effect works with 8-bpc and 16-bpc color. In After Effects CS6 or later, this effect works in 32-bit color.
Sometimes, it’s easier and faster to create traveling mattes by using a track matte instead of using the Set Matte effect. However, using the Set Matte effect provides some advantages over defining a layer as a track matte layer. The layer used as the matte with the Set Matte effect can be anywhere in the layer stacking order, unlike a track matte layer, which must be directly above the matted layer in the layer stacking order. Also, one layer can be used as the matte for multiple layers with the Set Matte effect. (See Track mattes and traveling mattes.)
Stretch Matte To Fit
Scales the selected layer to match the size of the current layer. If Stretch Matte To Fit is deselected, the layer designated as the matte is centered in the first layer.
Composite Matte With Original
Composites the new matte with the current layer, rather than replacing it. The resulting matte allows the image to show through only where the current matte and the new matte both have some opacity.
The Shift Channels effect replaces red, green, blue, and alpha channels in the image with values from other channels. It is GPU-accelerated for faster performance.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.