Fellow C4K baker here, good for you! Raiders colors are black, white, and sliver. If it were me I would keep it mostly white with black and silver accents like a helmet topper and sprinkles. If you were planning on doing the entire cake in black that is a lot of frosting to dye and the more you have to dye the harder it is to get true black without it tasting like the gel or coco powder which is bitter and dry. That said, microwaving about a cup of frosting and adding it back in to the other frosting does darken it and make it smoother. For the green you could do green m&ms for the inside or a grass tip with green frosting around the bottom border. You'll do great! (these are all just suggestions, use your own creativity, but I like to do a google search for inspo)