I use an Epson R260 (Claria 6-color dye) printer with a continuous ink system supplied by Echostore.com for proofing. I use generic storebrand Staples photopaper for this. It's not super-white; it leans to the yellowish side.
When I make prints using the so-called "Photo RPM" resolution setting (which I'm told means 2880 dpi) they have a cyan cast. When I make them with the "Photo" setting (1440 dpi) the colors are truer. I've fooled around to verify this, using, among other things, the SmugMug calibration image at
http://www.smugmug.com/help/calibration-1400.mg
Now the solution to my problem is obvious: use Photo, not Photo RPM. But my question is, why is this happening? I ask because it always helps to understand the equipment I use.