I think this may be an admission of my own fallibility but here goes: I've been playing with the MIS inkset in my old Epson 1400 and noticed that when I print using only black ink (K) the image is warmer toned than when I print using only the cyan (c, obviously) cartridge. The C gives me a wonderful, full range cold black tone.
Did I screw up last time I refilled the inks and put the K into the C, etc?