Ok, I've been running a NOS 50 shot for a couple weeks now just fine, checked the plugs last week and they looked moderately rich (goldish-brown color, no signs of detonation)

. Tonite I decided to do a couple runs but it was hella cold out. As a result my bottle pressure was at 630 (think I'm low on nitrous as well).
Anyway, when I did a run spraying in 3rd gear (at 4000 rpm) it would pull hard for a bit and then my car would slightly bog like nitrous was kickin in and out. It would still be pullin nicely but not as much as it should. I did a couple more runs like this when I realized I may be hurting something.

My question is do you think I could have fouled my spark plugs? What problems can come from running too rich without enough nitrous? Everything seems fine but I'm buying a bottle warmer asap.