I would say that all depends on how true to the game you want it to be. If you want something more true to the games steel base color, there's a cosplay guide for the Rookie ODST.
I've done ODSTs in several colors so really the sky is the limit on what you can choose.
You could do pretty much whatever colors you like for base colors, then just match accent colors to them.
I know you prefer not to use brown tan or grey as a base, but what I would usually recommend for base colors would be brown, grey, OD green or tan. If you plan to just spray paint your armor, It's always a good idea to start with your lightest color and work to the darkest one.
What construction method are you planning on making your ODSTs with?
me personally, i did red and black with an urban camo base, but its really up to you, and the sky is the limit on how much you want to put on the costume, as well as how much effort and time you'd like to put into it.