et-3760 will not print multiple color correctly.

The issue with these ET printers is that you still have the same printheads prone to clogging, with much harder access to clean the printhead when it occurs :/. If the cleaning cycle doesn't fix it, it's usually a clog needing a solvent designed to break the clog down with these Epson printers. You will need something like this. IMPORTANT: Epson has a more powerful "purge" (power flush) buried in the firmware, but DO NOT USE THIS! It burns a lot of ink and will end your waste ink pads early! Yours uses the $10 "serviceable (read: CHIPPED)" version they call a maintenance box, but still; it doesn't mitigate things like the platen pad getting trashed by this "feature". Until Epson releases a user-swappable platen pad assembly like the "maintenance box" which replaces the non-serviceable waste ink pad, I won't be comfortable using the power flush option

I don't have a SM for this one (or a source), but what you have to do is "start" a cleaning cycle to unlock the printhead (sorry, the old days where this could be done mechanically with no issue is over) and unplug the printer; this will let you move the head freely. Once that's done, lay down a lint-free shop towel or a paper towel in the platen area to catch the ink without killing your waste ink components. You will need to unsnap the printer's ink carriers and inject cleaner into the head; do this 2-3 times until it is clean. Once that is done, run a test page like this to get the ink flowing again. You could technically do a standard head cleaning, but this wastes far more ink than running a page like that to get the ink back in the system.

To avoid it happening again, run a simple page every week. Nothing fancy is needed here, you just need something to keep the ink flowing inside the printhead. Setting up something to print "TEST" in all 4 colors will do the job here. Do note some commercial programs like Qimage/Qimage One have a feature to automate this, but unless you are running photo prints that warrant a $120/$250 purchase set a reminder to do this on your phone or a recurring calender event.