Holobleeds are considered errors, you can read some general indormation about them in this great guide:
www.elitefourum.com/t/masters-guide-for-pokemon-wotc-corrected-errors-test-cards/29328/1
They can look pretty sweet, depending on the card and the severity of the bleed. Most of the time (again, depending on the set), there isn’t a huge premium attached to them.