Their color scheme fluctuated depending on the light they were shot in, both the Runner and the Resurrection Alien (as per the earlier incarnations). Seems weird to read, but the A:R Aliens had a lot of airbrushing detail on them too (you can see pictures of the suits being painted in the Alien Anthology extras), the photography of the film managed to not show much of these details; the same happened to the Runner. If you notice, the pictures showing those details are always in a neutral or green light; the Runner was shot in Alien3's photography (to that add the... poor compositing which erased plenty of the detailing of the Rod puppet), that managed to somehow cover them.