So, in tWoK, (I was unable to find a theory like this, but there may be one at the bottom), at the beginning of the end battle, Kaladin used a ton of stormlight, and his sskin went gray. This, I think could possibly indicate that his breath was transformed into stormlight, causing him to turn Drab. This would also mean stormlight can transform into breaths, which would make sense if Szeth is using Nightblood.