A lot of woman are actually experimenting with her haircolor and went at least once with that sexy one.

It all comes subconsciously.
Maybe you have already heard about "the red dress effect"- a phenomena which tells us that woman wearing red clothes (usually a dress) are perceived to be more sexually appealing than wearing other colours. Many studies have shown that men rate women wearing red clothing as being more interested in sex, hinting that humans may be conditioned to associate the colour with fertility.
The effect of red colour is nothing new. Woman dye their hair red, apply pinkish blush and bright lipstick for nearly 12,000 years. And what`s the usual gift for Valentine`s Day? Red roses...
One can see it on many primate females- when they become fertile, their estrogen levels rise, dilating their blood vessels and turning their faces bright red. This flush effect seems to give males the signal that it`s time to make their move.
Let it be a red dress, red lips, or red hair- it all sums it up into a sensual appearance.