This mode displays each intensity value as one of 256 shades of a single color. If you choose a basic color for each channel (red, green, or blue), you can display up to three channels. If you choose a compound color (magenta, cyan, yellow), you can only simultaneously display up to two wavelengths. The colors can only be combined so that red, green and blue are each assigned once.
If the Image window is not already open, open an image file.
From the Image window menu, choose View | Color to display the image in Color mode. If Color is not selected, the image is displayed in Grayscale mode.
Choose View | Select Image Colors from the menu to open Select Image Colors.
Choose a display color for each wavelength. To display each wavelength as a different color, choose either Red, Green, or Blue. Do not select Yellow, Magenta, or Cyan unless you only want to view two colors (or one color) simultaneously.
Click Done to close Select Image Colors.
Use the wavelength selector to display or hide wavelengths in the Image window.

To view the 4th channel (which is assigned to Black), select a color from one of the other wavelengths, which will then turn Black. If you keep the Select Image Colors window open, you can switch between displaying 3 of the 4 channels in Red, Green and Blue.