I am assuming the DE is Xfce because Xubuntu is a tag.
One way to do so is to create an empty .gtkrc-2.0 file in your home folder. It will be an ordinary text file but "hidden". In this file, you can paste the following content and modify it to your taste.

(If you already have an existing .gtkrc-2.0 file you can just append the stuff.)

style "xfdesktop-icon-view" {

XfdesktopIconView::label-alpha = 0

XfdesktopIconView::tooltip-size = 32



fg[NORMAL] = "#83aab7"     #was #83aab7

fg[SELECTED] = "GreenYellow"      # greenyellow

fg[ACTIVE] = "yellow"      # yellow

}



widget_class "*XfdesktopIconView*" style "xfdesktop-icon-view"

The second line governs transparency of the icon text background.

The third line controls the size of the tooltip that appears when one hovers the mouse cursor on an icon on the desktop.

The next three lines control the text color for different "states" of the icon. Both hex code and recognized words are acceptable to specify the color.

By the way, I have a plain black desktop and those colors suit me.

Depending on your set-up, you may need to just switch to another theme and back to see the change take effect or you may need to log out and back in again.

(This works for me in Xfce 4.10; it should work with 4.8 (which is what vanilla Xubuntu 12.04 has).)