This causes selected monochrome Breeze icons to turn white as this state is meant for when the icon is actually painted ontop of e.g. a blue highlighted bar.
Since the advanced icon configuration (where you could choose a custom hint color and other effects) has been removed in Plasma 5.13 and more importantly the fact that Dolphin always tints the icon in the highlight color disregarding any custom icon effects settings this is an acceptable change.

BUG: 398014

Changed icon size to 16px, selected a folder, folder icon was still there. You can hardly see the blue tinting with the 1px outline icons, though
Before