The Quill in each feather are where one will find the blood.
When this Quill is broken then bleeding occurs, and your bird can bleed to death.
Here's a link to help you to understand what is meant by Blood Feathers.
Broken Blood Feathers in Birds: First Aid and Removal
Here's another link with Pictures.
Blood Feathers
Here's some more good reading.
Welcome to Parrotdise!
I am pleased with you decision to clip your birds wings.
Folks can argue this topic and by all means this subject has been very controversial.
Many folks say "how can you clip a birds wings?".
I say "how can you take the freedom away from a bird period by caging the bird and or bringing the little animal into the home and kept as a pet"?.
If we must keep them in our homes "walls are cages also".
Best to protect them the best we can from injury.
Learn all you can about clipping, consult your vet.
Let us know how it goes.