Blood feathers are what newly emerging feathers are called. When a bird molts or loses feathers and a new feather grows in its place it emerges as a quill. The quill has a great blood supply to aid in rapid re-growth. This is perfectly normal and necessary for the feather to grow. If these newly emerging feathers should be damaged during this time of growth they will bleed like crazy. If a blood feather is damaged it needs to be plucked out to prevent a bird from bleeding to death. If the feathers are not damaged then they should be left alone. Plucking every blood feather out will leave a bird naked because you are essentially pulling out all their new feathers. The bigger the feather, the better the blood supply, and the greater the chance of hemorrhage if the feather should be damaged.
Hope this helps. Good luck.