I made some small tweaks in dolphins configuration window. I don't remember anything that looked like a folder color option. Somehow though all of the folders, and other icons such as the Discover / Dolphin app icon, have turned green. That's not the only thing that's green all of a sudden. The highlights, such as the selected item in the kickoff menu and the selected folder in the dolphin places panel have also changed from blue to green.

So, does anyone have any idea how to change the default color in Dolphin, and the rest of KDE from green back to blue?

OK, this is embarassing, but I figured out the issue. Nothing in KDE changed at all. All it was, was Redshift coming on just as I changed the Dolphin settings, making the screen redder. Blue folders + red tint from redshift = green color.

When I turn off Redshift, voìla! Blue folders in KDE again...