Here's a shot I did on a car I helped my friend/dad build a few years ago...Not a truck, but may give you some ideas on size, shape, flow or shading. On the Yellow, I wanted to get away from having too much Yellow in the flames...on Black this wouldn't be such an issue. The flames are outlined in 1/8" in a bright Apple Green. When I told them I wanted to use Green, the look was

but once a test panel was sprayed...there was no doubt! It looks JUST right. Not really apparent in the photo, but the flames are done in transparent Yellow & Orange (similar to a candy color). I've allways liked Blue or Purple on Black if using the traditional Yellow/Orange. Have fun! Hope this helps in some way, Lorne