To add another twist to what Ernst has said, and simply as an fyi. . . . .
I have been experimenting with dilute HP and Canon ink sets and either mixing, or coating prints, using MIS' gloss optimizer product. GO warms the print tonality, especially the a* value. This I assume, is why Cone Selenium always looked so "brown" on glossy media to me. I get the same warmth when I use GO to dilute HP's PK, which is actually a cool ink to start.
Gloss optimizer appears not to be truly "transparent".