I think if this were my bike, I would go with the black stripes to match the fenders. It would be a nice way to tie it all together.
What many painters..don't..do, is to seal off the paint line on the filler neck. Fumes (as mentioned) will get under it and start to bubble the paint. Tige mentioned using JB Weld, and that's something I've advocated for years now. Keep the paint line below the top of the neck, and just mask a line 1/8" above and below the paint line, swipe some JB over it and it will most certainly stop the gas fumes from intruding.