For those that want to dress as Katniss for Halloween, cosplay ou for a costume party...

Lets start with the book:

Katniss wears a a light green chemisier with her mockingjay pin, tawny pants, brown ceinture and a thin hooded black veste that falls to the thighs. Her hair is done in a braid down the back. She also wears combat boots.

If toi want to go totally accurate toi can mess yourself up a bit, a wound just above the eyebrow and flame-painted fingernails (For those that have read the book will know).
And since Katniss has black hair and grey eyes, if toi don't have the colour toi can dye your hair...