(Flashing imagery warning!)
If seeing me color this by hand is frustrating to watch, know that it's even more tedious to do in agonizing real-time :P
Procreate does have primitive bucket fill capabilities, but they don't even try to work properly if you're using a textured brush for your lineart. At the end of the day, it's $12 software, so I can't complain too much; it's still pretty beefy for the pricetag and sure as hell beats paying a subscription for Photoshop or CSP.