I suggest you look into color theory and specifically color spaces. Color spaces are the different models use to represent colors. The attributes that are actually described the the pixel will be dictated by the color space.
One of the most common color spaces for computers is RGB/ARGB. That is the format that many bitmap images will be in. Each pixel has a Red, Green and a Blue component and some sometimes an alpha channel is also represented.
Video and images are typically not stored in RBG however because there are other color spaces that can represent the same images, but compress much better. One of the common formats is YCbCr. YCbCr use a mixture of the luma(Y) components (brightness/intensity) with the chroma(CbCr) components (color) to represent the actual desired color.