any tip painting brunette.
I use tamiya flat black,or do I need some mix with other color?

I never use pure black on a figure, it doesnt allow for shading and makes other colours look dull and lifeless. Vallejo German Camo Black Brown is a good base for very dark hair, lighten with tiny amounts of golden brown and sunny skin tone. Use a VERY small amount of Paynes grey to darken

depending on the scale (and your eyesight)the definition of highlights and lowlights can be very blurred

Actually, "brunette", as it's name implies, is brown hair, making highlighting and shading easier. Black hair is usually referred to as "raven". Although Westerners can have black hair, it's more common to Asians, and brown hair, vice-versa. For black hair, a touch of blue could be added for highlighting; or a touch of brown.
ie; my wife is South-East Asian and her natural hair color is a VERY dark brown - black coloring is noticeably too dark for her. It depends on which ethnicity you want your figures to look.

Any advice on blonde hair ? red hair ? thanks

Red Hair: start with orange/red-brown; highlight with orange/yellow; shade with red-brown/dark brown:
https://www.google.ca/search?hl=en&tbm=isch&source=hp&biw=1600&bih=769&ei=hFKpWtPtB87KsQXV4LLQDw&q=red+heads&oq=red+heads&gs_l=img.12..0l4j0i10k1l4j0j0i10k1.2516.10034.0.14705.12.11.1.0.0.0.110.1007.9j2.11.0....0...1ac.1.64.img..0.12.1012....0.3qBfo7Rbk9Y#imgrc=_

Blondes; start with sandy dark yellow; highlight with same mix with increasing white; shade with same mix with increasing browns:
https://www.google.ca/search?hl=en&biw=1600&bih=769&tbm=isch&sa=1&ei=k1KpWo-cCpiJjwT6qLmoAQ&q=blondes&oq=blondes&gs_l=psy-ab.12..0l10.686267.691276.0.696610.15.14.0.1.1.0.300.1516.10j3j0j1.14.0....0...1c.1.64.psy-ab..0.15.1524...0i67k1j0i10i67k1.0.cAgIjUzAoNo

This is just a rough guide-line as there are many variations of both red, and blonde hair (many dyed!)