I have had a shop with gray cement floors and open studded walls (dark), gray cement floors and white walls, walls with the lower four feet painted a light brown to hide dirt, and white floors and all white walls, and this is what I have observed.
If you look straight out at the shop one third of your sight is the floor; one third is the walls, and one-third the ceiling. As you move you head around, your eyes are constantly adjusting to the amount of light received, which is related to the reflection off the background colors. To reduce fatigue, the walls should have a similar light reflectivity as the floor and to a lesser extent the ceiling.
If your walls are white, or a light color and your floors are dark this will cause your eyes to servo all day long as you move your head about. I would say, try to match the light reflectivity in choosing the colors; if the floor and ceiling are dark, choose a darker color for the walls.
The best situation would be if you could epoxy paint the floors white, AND the walls white, or some light color. When I did this to my shop I was amazed at the effect it had on the work environment and how much longer I could work in the shop before I felt the same level of fatigue. Even if you are welding on the floor or other dirty activities that will mess up the paint over time, the white painted floor will help with your vision in the shop.