The Histrogram Palette’s Visual Cues
When you’re using Photoshop’s Histogram palette (under the Window menu), not only can you see a histogram of each individual channel (select the All Channels View option from the Histogram palette’s flyout menu), but you can use color as your visual cue to quickly see which channel is which. Just choose Show Channels in Color from the palette’s flyout menu, and then the Red channel histogram will appear in red, the Green in green, etc.