It depends on what mode the image was last saved in. The Color Seration you are refering to is known as Channeling. Photoshop has much to do with the channels. The two most popular modes images are saved in are RGB(The most colors), and CMYK(Photographic Colors.) RGB has all of the colors that the CMYK has and then then some. The first has three channels, Red, Green, and Blue. The second has 4, Cyan, Magenta, Yellow, and Black. These are located in the Channels Pallette. The only problem here is that the values of the seperated color channells are represented in grayscale. What do you want to Seperate the color for? The image quality of a single channel is'nt usually near as good as the combination. It only makes sense, if you have a well balanced image the presence of just one of the channels is only 1/3 or 1/4 of the image. Each of the pixels in the image will be sacraficed. You could select the entirety of a channell, copy it, switch to the layers pallette, paste, and then convert the grayscale values to color with the Image>Adjust>Hue/Saturation>Colorize toggle. This would give you the option of coloring with 256 different tones. Or you can use Red(R=255, G=0, B=0) in the color selector to affect the Hue slider. That should be what you want. If you just want to see the image in a single color tone, Photoshop can do this also in a couple ways. First, with the Image>Adjust>Hue/Saturation>Colorize toggle via playing with the Hue slider, and the second via a modes known as mono/duo/tri/an d quardatones.