Do you mean what kind of paint? Or do you mean what color?
Paint type would be your choice. Acrylic mixed with liquid latex rubber has always worked well for me.
Paint color would really be up to you and your imagination.
The Predator skin has been portrayed in a wide range of colors. Shades of brown, red, yellow, green and even blue or purple have been used to great effect on many Pred hunters. Otherwise, it's kind of a tough question to answer.
If I were you, I would grab a few photos of either the P1 or P2 hunter and go for a light-brownish yellow for the base skin color. Then you want to get a few different shades of brown for light-colored markings and spots. And, finally, some very dark color like black for the darkest markings.