if u have a light coloured marker it shouldn't be a problem mainly for the following reasons.
1)the paints wipes easy
2)you should clean ure marker when u get home from every time u use it this is the best way to keep it bling mate i can vouch for that lol
3)no they don't look like crap when they get dirty cause if u do points one and two then all u have to do is wipe them after a messy game mate trust they stay clean.
All colours of marker go through the same anodising process so the finish will not be any more likely to dull or absorb crap than another colour.
Having owned a polished ( as in bare metal!!! ) RT mag for a while they are very easy to keep clean, 'cos the smallest spec. of muck will stand out a mile ( well you'll think it does!!! ) and you'll be in there with a cloth!