Did you start using aftermarket inks? Problem here unless using icc for high quality ink. stay away from cheap inks as there are no icc profiles. An icc profile tells printer what kind of paper is in printer so it will lay down proper amount of ink for that paper.
Using new imaging program? Make sure you use program or printer for setting colour, not both.
Reinstall printer to reset icc profiles as they may have been damaged.
Did you start using aftermarket paper? Problem here, unless you are using high quality paper and matching icc profile for that paper.
I have a R1800 that is the same as the R800, only that it prints to 13 x 19.
Hope this helps, Eric