it's an interesting design... but I have to say I'm finding it quite difficult to read.
At first I thought the gun handles were in fact some kind of flying helmet on the skull (the goggles don't help with that perception).
You need to differentiate a bit more between the colors your using on the skull itself and the colors you're using on the revolvers, either that or you require some harder shadows that lift them apart...
I know you probably want to keep this to 64x64 but I'd rotate the guns so the handles stick out too? S'up to you though...
I had fiddle...
Aside from the obvious, I fiddled with the goggles, the eyes (made them red [I like red] and increased the depth by increasing the shading around the orbits of the eyes and the brow of the nose), the nose [added some detail into the internal bone structure],
the teeth (you had amiddle tooth going on... so I removed it in favour of 2 nice big old buck teeth.), and the pallette, I've added some shading (rough like) where the skull cheeks meet the revolvers - and that's about it...
it's extremely rough - but just to give you an idea of how make your's a little more readable.
I hope that helps...