I worked up a design once for a gas-giant colony based on Buckminster Fuller's concept of a hot-air geodesic structure. Some nuclear power source would be required to keep the atmosphere inside heated--don't think sunlight would do it.

You select an altitude where the pressure is about 1 Earth atmosphere, and float there. Slightly higher pressure in living quarters would keep toxic atmosphere out.

This was years ago, before we had as many pictures of the outer planets as we do now, but I suspected Jupiter would be too stormy for this. Wasn't sure about Saturn. Additionally, Jupiter's gravity is almost three times that of Earth. All the other outer planets have a gravity quite close to Earth normal.

Not sure how much radiation you get down in a gas giant's atmosphere.

Big question though would be "why?" I could see remote science stations, possibly even manned for short times, but building a major colony seems a bit odd, given all the space out there on moons and asteroids. That's a lot of work to get "natural" gravity.