If the effect is worth it, it’s easy enough to anodize them your self.

I have some gold anodized rivets, I have not seen blue ones.

Usually they're 5/32" Brazier head rivets. These can be replaced with 3/16" Modified Brazier rivets if the hole has become oversized. For a given shaft size, the Modified Brazier is the smaller one and it's virtually the same size as the next smaller shaft's Brazier head.  e.g. The head of a 5/32" Brazier is the same as a 3/16" Modified Brazier and they use the same rivet set.



Length varies by the thickness of what's being fastened. You don't need to worry too much about buying the correct length if you just buy them long, say 5/8" or 9/16", and cut them with a rivet cutter to get to the 1.5x the diameter, protruding from the work. Some guidelines:


I've never seen anodized solid rivets. Maybe someone else has found them. Usually the more common anodized rivets are the pop rivet type. I'd expect it to be difficult to buck solid rivets without marring the anodizing if there is such a thing.
 

What are the dimensions of the average rivet in our boats? Anybody know of a source for anodized rivets?