What dmm says is true, but it looks like you have stumbled across a small bug anyway: It shouldn't tell you "cannot colonise ice planet" because you can - that's your own race's planet type. It should say "cannot colonise methane planet." Mail it to MM.
Don't scrap the game though, it sounds promising. Remember that your enemies have similar restrictions.
For a workaround, you'll have to find a way to encourage other players to colonise worlds that you want and then trade / steal the planets from them. It might not be easy gtting the AI to do this but let us know how you get on.
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SE4 Code:
L Gd! $ Fr- C- Sd T!+ Sf-- Tcp-- A% M>M+ MpD Pw RV Fq+ Nd- Rp+ G-
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