A word of warning to all : careless handling your X-acto knife can result in blood on YOUR uniform !
There were posts on this subject before. You may find them by performing a search on keywords 'painting blood".
From what I read in the past and my own experience, the candy red won't do the trick. Neither will the reddish browns of "dried" blood. The solution lies somewhere in between : bright red with a touch of brown. Just start mixing a few drops and see what you think of it. Smear a bit on your fingers (next to the accidental cut you just made with your X-acto) to compare.
Vallejo paints now have "gory red" as a separate color in their "game color" series.
Check your own paint jars collection first, though. Grab the reds and the browns, and start mixing a few drops of the one and the other, till the mixture pleases you.
Don't forget that the human body only contains about ten liters of blood. From this you can conclude two things :
- have that x-acto wound stitched when you are ready comparing colors. You may need some for other purposes.
- some modelers like to splash blood around vigorously. Don't. Try to use enough blood to make it clear that your soldier is wounded, but not too much so your model can't be mistaken for a victim of a horrible accident at the production line in Heinz" ketchup factories.