And this is one of them. By the time the K-4 became operational, the Luftwaffe had pulled out of Italy completely, leaving the air defence of the north to the ANR alone. So if you want to see a Karl in MAW, it has to be one of the 19 delivered to the ANR.
This one is W.Nr 330209 - if you go to this site: http://www.messerschmitt-bf109.de/
and look in the gallery of Bf109k-4 photos, first page, bottom row, on the right, you'll see it wearing its German delivery colours and Werk Nummer sprayed on the rear fuselage. It appears not to have served with the Luftwaffe, as the absence of individual number forward of the fuselage cross suggests.
You may be a bit surprised by the rather bright green I've used, though. Purely artistic licence, as nothing in the photo allows you to make the slightest concrete assumption about the actual colours used. This is RLM 83 Lichtgruen, one of two shades of green (the other being the more common RLM 82 Dunkelgruen) authorised for use in combination with RLM 81 Braunviolett, as here. I like it, in any case!