It's a little bit of blood that's still attached to the feather.
There are many things that can cause a bird to pluck and we often have to figure it out by trial and error. Often, the cause will never be found.
Do you think the bird is under any stress.........loud noises, too much activity in the household, sleep patterns disturbed, etc???
Also, what does your birds have in the way of toys and how large is his cage?
You may want to buy him a wooden lovebird nestbox and place it inside the cage........don't hang it on the outside........... and see if that will help take his mind off plucking. All my birds have nestboxes, some like to sleep in them and some sleep on top of them, but all the birds enjoy chewing and slowly destroying them. I consider them 'large' toys!
Thank you Axle for replying. I thought of blood when I first saw it, but it was so black I didn't know if it was or not. Nothing has changed for him recently, nothing that would cause stress. He has a very large cage and plenty of toys. He spends most of the day out of his cage with me. He is very loved and has plenty of attention. I'll try the nestbox. Thanks for the tip.
welcome to the forum
nice to have you with us
a happy hut for him to sleep and play in could also work
Did the vet do any test? There are a lot of medical reasons for plucking....kidney infections, giardia, (a parasite that makes them pluck under the wings) allergies, heavy metal poisoning....the list could on, the point is unless the vet did some tests....skin scraping, fecal test, blood test...he is only guessing. And no molt will cause bald spots! I hate when I here this answer, it means a lazy vet. sorry. The fact is MOST feather plucking is medical in nature and than turns into behavioral out of habit. And you will have a hard time figuring out and solving the problem untill you can rule out the medical.