According to RaptorFinder, the most popular colors for 2018 in order of popularity are:
Black: 25%
White: 16%
Leadfoot: 14%
Blue: 10%
Magnetic: 9%
Ruby Red: 7% - note that Ruby was late availability so pro forma popularity may be higher
Race red: 6%
Ingot Silver: 6%
With that said, I'm not sure if Raptorfinder includes custom order builds, or only looks at dealer stock orders. My truck is en route to my dealer but does not show up on Raptorfinder. As such, actual percentages may vary, with custom orders having different color preferences. I would assume leadfoot and black are the most popular custom order colors