BG rises when you've got a cold

I don't think so. Apparently non-diabetics do become more insulin resistant when under stress/illness, maybe needing 50% extra insulin, but their body automatically makes the extra insulin to control bg. Hence diabetes is often diagnosed during or just after an illness, because the impending-diabetic may be making enough insulin (or be sensitive enough to it) under normal conditions but can't cope with the extra demands when they're ill.