As inks dry their reflective properties change and the appearance of the
image changes. In my experience Canon inks are more susceptible to this
effect than Epson and I dimly recall this even being mentioned in the
otherwise useless instruction sheets that came with the Canon printer.
There should not be color shifts like what you describe.
An overly magenta cast to a print can be the result of misuse of color
management. If you are using Photshop, or any color managed program, and
do not have your color management settings correct, or if you do not make
the correct selections in the Epson printer driver, you will get a magenta
print. Properly made Epson prints should look color correct, depending on
your color management skills, out of the printer.
Another possibility is that you are viewing the prints under differing
ambient lighting conditions. The effects of ambient lighting on print
viewing can be enormous and often have to be considered in setting up
one's color managed work-flow. The ambient lighting can have a big impact
on how you calibrate your monitor as well as your initial evaluation of
the image coming out of the printer.