PJ Paints used to do KTM silver, but stopped doing it a while back. I went to one of those mix & match paint shops but the guy was a myopic SOB, bloody green would have been closer to the silver he reckoned matched the frame.
A lot of peope tend to powder coat the frames, and from what I recollect the "paint" on the original frame may be powder coat anyway - it's tough stuff but flakes off in lumps when rust gets behind it, particularly where the pegs are.
RTS