I never use my good dark reeds for double tonguing, I used an american style reed last night, and started triple/double tonguing as usual like I have been doing for three weeks now. I noticed that a little bit of blood was going onto the reed. This has never happened before, I might expect this from a dark stiff reed, but not from a light reed!
Your throat should not be bleeding from playing at all! When you notice blood get some tissue and place it in area in your mouth (along gum line, under lips, under/on tongue, etc) and see where the bleeding is coming from.
If your gums are bleeding you want to start flossing regularly, they will strengthen up.
As said earlier you need to confirm where the blood is coming from and do not assume. My first guess is that the lighter reed is clipping the bottom part of your tongue tip like a small razor blade. Expexially if you are using the french method. That is the first place I would check. Secondly I would check your gums (mentioned earlier) if it is not there then yes, it can be in your throat. It is not common but sometimes there are some very small capilary blood vessels that can come to the surface. With oboe there is more pressure than you realize in the intrathecal area and this pressure will increase for some players when they go into the double tongue mode and this extra pressure can cause those small capillaries to burst.
Again, confirm where the blood is coming from. If it is coming from the throat you should see a throat/nose specialist to confirm it is temporary or at least not dangerous.
In response to whoever suggest flutter tonguing - flutter tonguing and double tonguing are two completely different techniques and totoally different results.
im sorry to hear about this issue but i recently had a piece i had to flutter tungue i couldnt ever get it down tips from anyone would be nice... oh and i would also like to know you opinions on what kind of oboe i should look into im planning on playing for FOREVER!