Is there such a thing as blue-green colourblindness?
Our eye's blue detector is very old. It came before the rods and the red-green detectors. It is almost as old as multicellular life. The blue opsin has been theorised to have served as a precursor to photosynthesis.
Our blue cones are somewhat separate to our green and red cones. There are less of them in our central vision, and you can identify them in a stained retina under a microscope by their distinctive nerve connections. We have no blue detectors in the centre of our vision. There are some people with defective blue vision. There are genetic variations (see Oliver Sacks' Island of the Blind) that knock out all three detectors, leaving only the rods. But I know of no cases of blue and green cones being knocked out, leaving the red. it is possible to get some unfortunate with deuteranopia and tritanopia, but they don't go together.
I would be suspicious of evolutionary explanations, particularly short-term ones. Old-world monkeys developed three-colour vision millions of years ago. This is sometimes said to give an advantage when picking fruit. But red fruit are available in season when there is lots for everyone. Something that gave a survival advantage might be expected to work when food was scarce, or for some other reason such as recognising camouflaged predators. What do we actually use our blue vision for, anyway?
Try something else. We have a macular yellow dye over our central vision. There is still debate as to what it is for. It probably protects our vision against UV damage, and filters out blue (which we have no sensors for in our macula) leaving our red and green sensors without interference from the blue. Not having it (macular degeneration) is a bad thing, but the amount of macular dye varies from person to person. If vampires had much more macular dye (and the amount we have varies a lot) then they would not see blue.