Color Channels of an RGB Image
Normally, images are thought of as being two dimensional. In truth the majority of images are actually stored as a grid of pixels where each pixel holds channels with the amount of the colors red, blue, and green to display. This means that an RGB image can be thought of as 3 dimensional with the different color channels making up the layers.
Explore the image below to see how the original image on top is broken down into its 3 color channels. Note how the white stripe on the track is clearly visible in all 3. This is because white is the result of all the colors while black is the absence of them.