I also bruise sometimes, really light but I can see them.
yup i bruised a few times... its healing now but it look nasty
I definitely bruise on my stomach as well .. i've also noticed that it was on one side (usually the right side) and not the other. It was suggested to me that it was because of the bacteriostatic water. Also, from my observations, i've noticed that if I sit down to inject myself it will leave a bruise as opposed to standing up? It could just be a coincidence.
I've inadvertently hit a small blood vessel two or three times leaving a bruise. Other than than, no bruising whatsoever I give my shot in the tummy, too.