Anime characters with either purple/black/brown hair colors must be female and not to young.

Karen from Mermaid Melody Pichi Pichi Pitch.She has 18 years old.

Kagami Hiigari and Tsukasa Hiigari from Lucky Star. Both are 18 years old.

how about this doctor from MONSTER she has black hair

Yomi has black hair :3

Yuko Ichihara from xxxHolic

Roux Louka from Gundam ZZ
You can watch the show here, starting with either of these episodes:
Episode 1 is a clip show, I recommend skipping it: link
And start with Episode 2 instead: link

After that, maybe you can answer this question:
link

Kyouko Kirigiri. Someone had done the math (since they never revealed the true ages of the characters), making her around 18-20.