I've made a few custom 1:64 scale Hot Wheels cars for Hellcat/Demon owners. I've recently dove into the larger 1:24 scale diecast of the Challenger Hellcat Widebody (before the Dual-Snorkel hood), same body as the Widebody Scatpacks. I plan on making Trackhawks sometime in the near future. I use OEM colors when possible; I currently have: F8 Green, B5 Blue, a bit of Sublime Green, and Maximum Steel.
My latest completed project is a batch of six (6) 1:64 scale SRT Demons in B5 Blue (no sunroof and no black tops). I'd say that they're very detailed given the scale. I have yet to design their cards. I'd love for these to owners with matching spec Demons.
My favorite colors are F8 Green followed by B5 Blue, then Plum Crazy Purple, Indigo Blue, and Jazz Blue.