Thanks for the answer!
So, assuming this is a poison effect (that may be another debate), a insinuator with this:
"Stubborn Health (Ex): At 3rd level, an insinuator takes only half damage from diseases and poisons, and none of his ability scores can be reduced below 1 by these effects. This ability replaces plague bringer."
Insinuator takes 1 CON damage, but halved and rounded down, every minute, so could wear the paint with no penalties?
The war paint is made with realgar, which is classified as a poison. [See Alchemical Reagents.]
The Insinuator's Stubborn Health will slow but not stop the poison. Wear the war paint for two rounds and take 1 con damage. Four rounds for 2 con damage. The damage is based on the total time you wear it, and the ability is not resisting but slowing the damage.