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

Lets start with the book:

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

If u want to go totally accurate u 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 u don't have the colour u can dye your hair...