Just about everything you ever wanted to know about painting your helmet is is in TDH somewhere! Seek, and ye shall find the answer to all your questions
Enamel paints are just fine, in fact, there seems to be a wider selction of colors if you use enamel. Yeah, painting your own stuff is 99% of the fun! You can definately spray your helmet w/ silver 1st, then mask parts you want to show through with either rubber cement, masking tape, or even mustard I hear
then spray your other colors. when all is dry, the fun begins. peel off your tape, or use a rubber cement pick-up eraser to remove your masking, (depending on what you decide to use for mask.) Instant battle damage. This is just one method of many. I leave it to you to discover more on your own.
Have fun