And if so, why do you know?
I think I'm O-neg, but frankly I'm not 100% certain. I seem to recall my parents telling me that once as a kid, but I can't say I've ever had it checked (well, I'm sure I have, but I haven't asked what the result was). I keep meaning to get a friend to do some baseline bloods on me as a general healthcheck; I might get them to check my blood type at the same time. Just curious.
I'm pretty sure (human) blood is always red.
Look at your veins. Most of them are blue. The blood usually doesn't turn red until it reacts with oxygen.
That said, a lot of your blood is indeed red.
Seriously, blood is always red. Trust me on this.
Venous blood is a much darker red than arterial blood though. Veins appear blue-greenish because of skin/pigment/tissues in between.
vial. Vile means something else altogether.
I prefer phial, personally, because I'm snotty like that.

Like others have said, for anyone receiving proper medical care, there's really no reason to know, as you'll always be cross-matched if you need blood. If it's a major emergency and it can't wait for the cross-matching, they'll chuck O-neg in you as it's a universal donor type in those situations. There's always a couple of units swilling around in a fridge somewhere in the ER. At least, there used to be in my day, I don't know if they've got quick enough at cross-matching to avoid this emergency need nowadays. ZR or StolenThunder will be able to tell you what happens these days, I'm sure.