There are two basic digital color models:
RGB (Red / Green / Blue ) Color Model - combines the three primary colors to produce an array of colors.
HSL ( Hue / Saturation / Lightness ) Color Model - colors of each hue are shown a scale from white at the top to black at the bottom.
Color computer monitors will use mixtures of red, green, and blue light. The HSL color model is often used for the selection of colors.
The RGB color model will often be represented as a cube, with red growing in degree along the width of the cube; blue increasing along the length of the cube; and green intensifying with the height.
The HSL model is represented as a cylinder, which each hue arranged around the axis, varying in degree from white at the top, and black at the bottom.
In Excel these color models can be seen in the Styles section of the Home tab. Click on the drop down arrow and then click, 'New Cell Style'. Then click Format, and on the Fill tab select 'More Colors . . .'. On the custom tab, you'll see you have a choice between RGB and HSL in the color model menu.
With the RGB model the higher the number of any color (on a scale of 0 to 255), the greater it's intensity. Setting red, green, and blue at zero will produce black; setting each primary color at 255 will produce white.
With the HSL model, the higher numbers for Hue represent the violet end of the spectrum and the lower numbers red. The Saturation setting will give a pure color at a maximum setting of 255, and a grayed out one at zero. The luminance or lightness setting makes colors lighter for higher numbers.
An alternative color model is CMYK (Cyan / Magenta / Yellow / Black ) which uses the subtractive primary colors in combinations to produce various colors.