I tried that back to black stuff and it really didn't work too well for me. It looks great in the first 5-10 mins, then it started going back to its original color lol. I used the armor-all original shine and that is holding up great.

 

I've used a meguiars product called ultimate black(I think).
It works great on my lower valence but anywhere else it sucks. No matter how well I get rid of the excess, it always runs onto the paint. It doesn't matter on the valence because there isn't anywhere for it to run.

 

Any liquid is not going to be a long term solution. I've tried every product under the sun. Some of the more expensive products will soak into the plastic a little bit, but is still able to be washed off.

Search YouTube for the heat gun method. I haven't tried this but apparently it lasts longer.

Ultimately you will have to buy new trim of you want a long term solution. It is possible to paint them, but if you are hard on them, they won't hold up.