I painted a wall yesterday (blue) with a new roller, pan, and liner. I wrapped the roller in a plastic bag and there was minimal residual paint in the tray. I left it out over night. I put paint in the same pan this morning and noticed as I rolled it onto a portion of the wall that it was a bit whiter than the old coat. I don't remember if it was quite that white when it went on originally. Could this be just because I'm applying the paint onto the new color and not a white wall or is it more that I should have cleaned the liner, or even that I should have replaced the roller? I tried a fresh roller and seemed to get the same response. Heck, maybe I just need to put some more elbow grease into stirring the paint. Any tips? Thanks
Your suspicion is correct. You've rolled a second coat, which often makes color more bold or intense.
It's common practice to wrap trays, rollers, and brushes as a set overnight. It's not a problem.
Fresh paint being applied is usually a slightly different color than a dried coat. You notice the guy at the hardware store hits his paint sample with a hair dryer before comparing it.
I half wonder if paint companies do this deliberately as an aid to the painter, to help you distinguish dry from wet.
It will also be a different sheen, as most architectural coatings are flattish and wet paint will be a high gloss.
Also, I have never met a pastel that is opaque on the first coat (and almost all architectural coatings are pastels). If your previous color is at all dissimilar, the second coat will cover better and the old color will bleed through less, which will appear as (and actually be) a change of color.