As well as the RGB components already described there is a fourth, optional, component, that you may wish to use. This is called Alpha and forms part of what is known as an RGBA color. Alpha essentially indicates how opaque a color is. It ranges from 0 (completely transparent) through to 100 (completely opaque). Rather than being a color it modifies the color.

Generally, you do not use the Alpha component when specifying colors. However, you may need to:

  • Insert an Alpha channel (see below)
  • Find out what the RGBA color is at a point