Would I have to use a new paint tray liner after only one day of I left it out overnight

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