Color fills our world and we marvel at the shades of flowers and sunsets. Color has almost an emotional quality, yet it is difficult to describe in simple language. In fact, we can not describe red, for example, without saying its like something. So, we say red like blood, green like grass or leaves, and blue like the sky.
Some colors go together.
Combinations of red and blue make purple. But, there are no blends of red and green or blue and yellow. There are no reddish greens or bluish yellows and there are no names for these color mixtures. Red and green are opponent and so are blue and yellow. This is the first clue that some colors are processed differently and there are two separate pathways by which our visual systems process color.