Erm, yup... I used Hammerite once on GFs Corsa and whilst it looked OK for a bit it didnt last very well. DFoliatec, tried and tested is hardwearing with a good finish.
Wouldnt recommend painting over it as it doesnt stick well to itself (i.e. it may well flake off quicker). If I were you, Id try to get the right colour first time as stripping the stuff is a nightmare!
I thought about red but decided Silver would be more subtle as mentioned above... I only wanted to smarten them up, not make a feature of them. Becides, behind the standard alloys you can hardly see them as the spokes are so fat. Once Ive got a nice set of rims on then they should be more visible.
Good luck to anyone doing this and my only 3 tips are... clean the caliper well with wire brush and spray supplied. Apply TWO coats and allow first to dry for 2hrs as recommended before applying second coat. Leave that 2hrs before replacing the wheel. Finally, Dont mix more paint than you need for each wheel as after about 6hrs mine started going quite sticky in the tin, was like painting with jam toward the end. Suggest mixing half the tin and doing one side, then mix the remainder and paint the other side.