It takes a while for the culture to fade and allow you to colonize, the best thing I found to do was to leave a ship or two behind to prevent the AI from re-colonizing, and then keep moving the bulk of your fleet forward. You need to be knocking out broadcast centers to deplete the influence, so you need to bring a large enough fleet to be able to mow through several planets with relative ease, otherwise it'll be real slow.

Your capital ships *should* also help drop influence faster, the tooltip says they slow the spread, and I imagine that also mean they contribute to the drop once the colony is destroyed, but that's something I can't really confirm by myself

I think I made the mistake of taking out the home planet first, as the longest oldest planet the culture never faded away to allow me to colonize it, I'll reload and try another outlying planet first and try and crack into the system that way.

I don't remember. There was at least one broadcast center. I think most of the stuff in orbit was gone before the colony was destroyed, so the culture was probably already decreasing by the time I was looking for it.

Are you playing the most recent version? What you are describing should not happen in the current build -- the planet should be yours long enough to build a broadcast center, at the very least.

There was a beta two patch with that (much needed) feature! BUG ALERT!

Orion, do you have a replay that shows the planet instantly flipping?

Send some American's over to the enemy; that should destroy their culture.

I now have a record of the colony flipping, how do I get it to you?

Email it to [email protected] witha note about what happens (and when and where in the replay), and a note that the colony prohibition needs to be extended a bit longer since instaflips are still possible right as it expires.