Bruises are consistent with an accidental puncture of the vein by the trochar while being inserted. It's not the nicest thing, but they happen. Damage may be done to a vein by infused medications, that may be corrosive. This is why some meds have to be infused over long periods. If there is damage from running in such a medication too fast the primary symptom is inflammation, which is characterized by redness, extending the length of the vein, or at least in a line from the medication entry point. A bruise, in the other hand, usually represents blood leakage from a specific spot, usually no more than an half inch or two up from the trochar entry point. The bruise is not normal, but should heal, as will the vein.
Take a piece of banana peel and tape it to the bruise yellow side out. Should clear it up.