Right then... I'm going to try to get through this reply without in descending into Frankie Howerd territory. The Progress is one of the few razors on my 'to buy' list, I had one years ago but lent it permanently to my brother in law as I wasn't satisfied with it's length (stop it). When I do get the long handled version I intend to paint in the numbers and markers etc. and I was wondering what, if anything, to do with the knob (ooh no, please... titter ye not).
Over at B&B there's a thread by someone who actually used dye to change the colour of their knob. If I find it, I'll post a link but it seems like the best and most permanent way of altering it. If that's what takes your fancy... (Oh, well, please yourself).
http://badgerandblade.com/vb/showthread.php/44495-Improve-look-of-Merkur-Progress
Found it!