I use 303 for that. Both to clean off the residue and to treat the rubber making it black again. Then afterwards if you keep putting it on every week or so for a few weeks it'll soak into the rubber to where it wont take any more. At that point it's like brand new rubber (the main ingredient is actually a part of rubber) and will stay like that for several months.
I just retouched my window trim for the first time since the spring, and it really wasn't bad at all, I just had some time on my hands after a wash.
All these rubber dressings are the same main ingredient (PTFE), just at different concentrations, and 303 has the highest concentration. Megs
trim detailer is #2.
Forever Black is a dye that IMO looks a bit more like ink. It's a blacker (slightly blueish at first), more of a surface coating, where the others are more satiny and natural looking. I like the look of 303 better than FB but it's really pretty close. And the FB doesn't require repeated applications.