Open the folder in Finder
Right-click the folder and select Get Info
Click the folder icon at the top left of the Info window
Press Command + C to copy the icon
Open Preview
Go to File > New from Clipboard
Open Tools > Adjust Color
Change the color as desired
Press Command + A to select the image
Press Command + C to copy the edited image
Return to the folder’s Get Info window
Click the folder icon again
Press Command + V to paste the new icon
Close the Info window
Repeat for other folders as needed