This is a friends garage in AZ. The flooring is Racedeck, 12x12 rubber tile especially for a garage. Personally I’d look into it in place of epoxy. Easy clean and it drains though that’s not much of an issue in AZ.

Here’s mine in snow country

What will you be doing in there? If just parking cars and hanging out then you can do just about anything. If you'll be working on stuff then a white ceiling (SW7757 High Reflective White is best). Walls can vary but a light to medium grey and as neutral as possible is easiest on eyes.

my dream garage would be a nice simple medium grey flooring and white walls -- like opaone said, to reflect as much light as possible so I can work. or perhaps this bluish-grey floor:

I envy that you get to do this. my garage is a glorified shed. uninsulated, no drywall, and I'm pretty sure it's built out of dust held together by 50 years worth of cobwebs. they're load bearing webs now.