always willing to accept money, BUT I might have zero experience with your machine, i think....still uncertain what it is aside from a mimaki.
always willing to brainstorm issues for free on this forum, however.
besides, keeping the thread updated is helpful since others may be able to chime-in with better advice than I may have to offer.
I just enjoy diagnosing stuff, because puzzles are meant to be solved....and printers were designed to work
back to the OP, however, until I know what machine it is... the most common source of complete color dropout in a printhead could be a thousand things besides a gunky/clogged printhead: ink pump, ink line, damper, printhead, printhead manifold, capping station, wiper, etc. and that's even before you get to potential electrical issues like ribbon cables, encoder strip/sensor, boards, printhead , etc.
best way to start, is at the beginning.....
printer make/model?
when was the last time you remembered printing perfectly?
what happened between then & now? did you perform any of your own service work? unplug anything, fiddle with anything? head strikes or crashes? miss a few weeks of maintenance?