I'm looking to build a xeno suit from the monsterroom kit soon and am gathering supplies for the project. I've been looking around to see what other people have done, but does anyone here maybe have good references for what has is considered "official" colors for the xenos?

"Official" is a tricky term. Like with most props from this film, you have two choices: How the prop actually looked vs. How it appeared on film.

Whole thing was shot with a blue filter, distorting a great many things. (brown bess looks olive drab, some olive drabs looked black, etc).
That combined with the lighting made most of them look black with blue highlights. In actuality they were black with brown highlights.

I believe the black /gray scheme and black/blue scheme outnumber the black/brown in costumes I have seen out at events, but all 3 are perfectly acceptable.

here are some images of actual props just for reference (most from propstore auctions of the original item)

Just come up with a back story on your build to explain the color. That helps if folks question the why of color. Make it your own and own it.

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The impossible takes a while longer and goes over budget too...

Those are some good pictures!

I think as far as screen vs. actual prop colors go, I'm trying to think of what giger or fox would consider "canon" as the colors of the xenos, so I've also considered sources like toys and the alien in Alien: Isolation, since that might offer a less "filtered" look like the movies and maybe show the "true" colors, if that makes sense.