Changing the default cream-yellow color to some other like red or blue will make the folder ... You can assign your own icon to the folders only from ICO, ICL, EXE, DLL, CPL or BMP file.

You can set a dark or any icon of your choice – but the images have to me in the .ico format. Read: How to change File and Folder Icons. As an example, let us change the icon to a dark one.