I played through a quick game the other night, and in the process I received the aquatic colonization tech from another race in a trade. I noticed after that that the aquatic planet I wanted still had a red icon on it. "Hmm," I thought, "maybe it's just a display bug." I moved a colonizer over to it, and nope, couldn't colonize.
A while later, I researched the advanced aquatic tech, and the planet went yellow. I colonized it and played out the rest of the game with a 50% penalty on the planet. When looking at the tech tree viewer, I noticed that the first aquatic tech was missing any icon on the bottom, in the place that would usually be showing the +50% bonus. So by trading for the tech, I actually crippled my ability to colonize aquatic worlds! That's a bit of a bug there, so consider it reported.