Widetrack gave you some very good advice but there's a part of his advice that is the most important and that is doing a test panel.
Always do test panels before you paint, especially if you are trying something new or using a product you aren't familar with. This is where painting can be fun, you get to play around, experiment, have fun with your project.
Try both the gray and silver in test panels. Make some test panels with some spray can primer. Use old fenders, or hoods or any kind of junk spare sheetmetal. Heck even a piece of plywood can work.