White, something in a higher sheen would help bounce more light around too.

Thank you. I agree about the light color. I was concerned white will show dirt and be hard to clean depending on the finish. It's just drywall now.

My last house had a white garage and it looked dirty in a short time. Have you thought about staining the block? Stain soaks into the block and will not peal in time like paint. Stain comes in many colors. Our block in our garage is stained with redwood deck stain . The little bit of drywall is white, and the trim and floor is gray.

What color is your car? LOL. Seriously, although white is bright and refreshing, there is no reason why you can't be bold and paint it a cheery, uplifting color. The garage is usually the last "room" you see before leaving in the morning for work, and the first room when you return. We do all kinds of chores in the garage, so why not paint it your favorite color, something that will bring a smile every time you get in and out of the car? While looking at real estate listings, I saw a pink garage!

White, and add plenty of lighting!

Higher sheen does NOT bounce more light around. It's a simple matter of physics.

The same color of paint in two sheens will bounce exactly the same amount of light.

Higher sheen will be easier to clean, but that's it.

Make it white, and have at least 2 light sources spaced apart so that one fills in the shadows of the other. That's easier on the eyes.

Yep, what tatts said.

Even the highest, shiniest sheen doesn't help propagate light through a space because the substrate/paint combo does not make a good reflector; it's not smooth enough, not reflective enough.

What you get with super shiny paint is spots of glare, there's no significantly measurable light distribution from the surface. The spots of glare make people think it's distributing light because it seems logical and it kinds looks like it is.

If it's attached garage, then I like to paint the inside a color with a high-ish LRV to coordinate with the exteriror. Lots of times we use the same color as the trim which is often a white, beige or gray.

Paint the walls Dirt Grey. Provide bright light bulbs.

Flat paints will diffuse light more, but the same amount of light is being reflected around. Flat paints appear flat because the pigment is ground very coarsely. When light hits it, it scatters in all directions. Gloss paints have finely ground pigments. When light hits a gloss paint, it reflects more or less uniformly in one direction, thus appearing shiney. These tightly packed small pigment particles also account for gloss paints being more moisture resistant and easier to clean.

I like white walls because I can see the black widow spiders better. Windows and good lighting are important. In my area, black widows are a year-round problem. The drought has cut down on their number. YMWV.

Bare concrete block? I just used this product to paint the exposed concrete foundation inside our garage. Covered nicely in one coat.

Our walls and ceiling are drywall and painted white. Prefer that color to brighten the space.