bloody mess

A hematoma is a collection of blood under the skin. This happens when you get a bruise. It looks purple through your skin, in part because the blood is not oxygenated after it has collected under the skin, giving it its dark appearance. (Freshly oxygenated blood is bright red)
An IV site is deemed to be "infiltrated" when fluid is no longer moving smoothly into the vein and back into your system, but when the vein becomes blocked or when it "blows", the fluid leaks into the tissues surrounding the vein, causing swelling and potentially causing a "goose egg", which is a lump caused by fluids built up under/in the skin.
When your patient is getting a blood transfusion and the iv site infiltrates, the result is a huge goose egg hemotoma, which is basically a big huge ball of blood in their skin. If, theoretically, this happened to a patient I was responsible for, the site of the huge welt of bright purply-red blood through her thin skin, the very idea of it, and the trickle of blood leaking out of it, would be terrible enough for me to have to sit with my head in my lap and be brought sprite by amused nurses.
HOWEVER, if this theoretical event happened on my last clinical day in this rotation, I think I would get over it. Which it did. Which was today. YAY!