We had an Epson 1500W which packed up and, to tide us over, we bought an ET2650 which obviously reduced us to 4 colours.
We had a lot of problems with blues appearing purple and stumbled across a solution online which, I think, had nothing to do with sublimation.
If you look at the colour readings in Photoshop you will see the CMYK readings next to the RGB ones. Adjust the Magenta to be 30% less than the Cyan so if, for example, the Cyan is 90%, reduce the Magenta to 60%. The RGB values will automatically change. This should remove the purple appearance.
The other thing we found if trying to print a purple(ish) background was to "Select - Select by Colour Range" and use the eyedropper to pick just the purple parts.
Then "Adjust - Brightness" and lighten by 30% or more which affects just that colour.
Much better results for us so might be worth a try.