Unless the hard paint only applies to the metallic stuff - it's entirely possible that the non metallic colours don't have a thick clearcoat? I know the Platinum Grey finish on mine is as stubborn as hell to work on - even full speed on a PC with any of the Menzerna polishes doesn't take much off.
 
ah of course, yours is the electric blue colour or what ever they call it. Is that non metallic then?

if there is a difference between the non metallic and metallic paints, thats interesting, although thinking about it, I would presume the metallic paints are harder with the extra lacquer and any pearl additives in the paint