They only way you will get black text with folders is in Icon view inside a Finder window. There is no solution to set the text of Desktop folder icons to black. Been that way for years, with plenty of frustrated posts on the Internet and here.
What I do to improve on this situation is to use a darker image as wall paper, and in System Preferences : Displays : Color tab, I pick a different display profile to improve the contrast and apparent sharpness of the folder font. You may have to uncheck Show Profiles for this display only to allow a wider selection. You might also consider clicking on the Desktop, and pressing command+J (Show View Options), and bumping up the Desktop font size to 13 - 14 pt.