Open your indexed-color image in Adobe Photoshop on desktop.
Last updated on
Sep 30, 2026
Learn how to modify color tables to remap colors, create gradients, and assign transparency.
Customizing indexed color tables gives you precise control over the limited palette used in indexed-color images. This technique works particularly well for pseudocolor images—scientific or medical visualizations that display data variations using color rather than grayscale—by mapping specific color ranges to data values.
Use the Color Table dialog to modify colors in existing indexed-color images. The dialog displays your image's complete palette as a grid of color swatches, allowing you to edit individual colors, replace color ranges, or apply predefined schemes. Your image must be in Indexed Color mode to customize its color table. To convert RGB or Grayscale images to indexed color, see Convert a grayscale or RGB image to indexed color.
Edit individual colors
Select Image > Mode > Color Table.
Click any color swatch in the grid to open the Color Picker.
Choose your replacement color and select OK.
Repeat for additional colors, then select OK to apply all changes.
Replace color ranges
Select Image > Mode > Color Table.
Click and drag across multiple swatches to select a color range.
In the Color Picker, choose the first color for your gradient and select OK.
When the Color Picker reopens, choose the last color in your gradient, then select OK.
Photoshop creates a smooth gradient between your two colors across the selected range. This technique works well for creating smooth color transitions in pseudocolor images or applying temperature-based color schemes to scientific data.
Assign color transparency
Select Image > Mode > Color Table.
Select the Eyedropper tool inside the Color Table dialog.
Click the color swatch you want to make transparent or click that color directly in your image.
Select OK to apply the transparency.
Note
You can assign transparency to only one color at a time. Selecting a different color for transparency removes transparency from the previously selected color.
Apply predefined tables
Photoshop includes several preset color tables designed for different purposes, from scientific visualization to cross-platform color consistency.
Save custom tables
Select Image > Mode > Color Table.
From the Table menu, choose one of the predefined options.
Preview the result in your image and select OK to apply.
Available predefined tables
- Custom: Retains your current palette for manual editing.
- Black Body: Simulates colors emitted by a heated black body radiator, progressing from black through red and orange to yellow and white. Useful for thermal imaging.
- Grayscale: Distributes 256 shades evenly from black to white.
- Spectrum: Displays the visible light spectrum from violet through blue, green, and yellow to orange and red, as if light passed through a prism.
- System (Mac OS): Applies the standard 256-color macOS system palette.
- System (Windows): Applies the standard 256-color Windows system palette.
Alert
Applying a predefined table replaces your current color table entirely. Any custom color modifications are lost unless you save the table first.
Save custom color tables for reuse
You can save customized color tables as. ACT (Adobe Color Table) files for reuse across projects.
Save a custom color table
After customizing your color table, select Save in the Color Table dialog.
Choose a location and enter a descriptive filename.
Select Save to create an .ACT file.
Load a saved color table
Open an indexed-color image.
Select Image > Mode > Color Table.
Select Load in the Color Table dialog.
Navigate to your saved .ACT file and select Open.
When you load a different color table, Adobe Photoshop remaps each pixel to match the corresponding position in the new palette. This can produce dramatic visual changes depending on how different the two palettes are.
You can also load saved color tables into the Swatches panel by selecting Load Swatches from the Swatches panel menu. This makes custom color sets available across all color modes, not just indexed-color images.
For more control over color adjustments in other color modes, use the adjustment commands under Image > Adjustments.
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