I designed these paint holders to store my paints on the pitched ceiling of my shed, but they'll work on a vertical wall too. They could be stuck to a wall, but they have countersunk screw holes for easy fixing. 

Covering most sizes of paints, pigments and thinners you'll likely encounter, including those from Vallejo, MIG, Ammo, Tamiya and more, I've also included a holder for Halfords paint pens, which are really useful for fine work.