Judging by the sort of glossy enamel finish, I would say they are powder-coated. You could try DIY powder-coating but the results may not be satisfactory. However, you can probably find a local shop that can powder-coat your Vex pieces for you. I recently had some steel stairwell light vent covers re-powdered white, and they looked great. While powder-coating will hold up better than spray painting, over time it can chip or scratch, especially with the Keps nuts. I also wouldn’t advise powder-coating or painting parts like slide rails, as the finish could add extra friction.