Why do we wear colorful clothing.

Why do we wear cloths at all in climates where its not necessary? Or anything but the simplest coverings. Because we want to.

To attract Hummingbirds? My shirt with bright red flowers does it all the time, at least in the summer.

Colors are fun, and certain colors can make you feel certain ways. All black is usually worn at funerals, or by emo teens. Bright red in certain parts of the world, means fertility. White for a bride means pure and chaste.

In the winter when all I see outside is white skies, white streets, barren trees, and no color, I wear more colorful clothing because it cheers me up.

IT is to distinguish ourselves from the crowd. Early on it was, and arguably still is, a sign of a person's fitness as a mate. Having exclusive clothing and or excluisve colours shows that you will be able to provide well for your offspring. A stone age person wearing a lot of deer hides, would be better then that slouch with a loin cloth out of woven tall grass.

Historically it is all about getting a mate and moving your genes to the next generation.

Why in the modern world. It is how YOU display how YOU want to look.

Sometimes colorful clothing relates to ones culture and traditions.
Sometimes colorful clothing results from how a person feels.
Sometimes it also means or denotes the way a person wants to carry himself
Sometimes its just trend.
Sometimes you don't know how to match so you end up wearing a rainbow :p
Etc etc etc, many more reasons.