If you're using the icon view, and would like to change how the text looks,
you have three things you can change: the opacity (transparency) of the
rounded text background, the color of the rounded text background, and the
color of the text itself.
You'd want to add something like this to your ~/.gtkrc-2.0 file:
style "xfdesktop-icon-view" {
XfdesktopIconView::label-alpha = 75
base[NORMAL] = "#00ff00"
base[SELECTED] = "#5050ff"
base[ACTIVE] = "#0000ff"
fg[NORMAL] = "#ff0000"
fg[SELECTED] = "#ff0000"
fg[ACTIVE] = "#ff0000"
}
widget_class "*XfdesktopIconView*" style "xfdesktop-icon-view"
The first entry sets the opacity of the rounded text background. The allowed
values are from 0 (totally transparent) to 255 (totally opaque).
The second three entries set the color of the rounded text background.
* NORMAL sets the color for the regular, unselected state.
* SELECTED sets the color for when the icon is selected, and the desktop has
keyboard/mouse focus.
* ACTIVE sets the color for when the icon is selected, but the desktop does
not have keyboard/mouse focus.
The final three entries set the color of the label text. See above for the
differences between NORMAL, SELECTED, and ACTIVE.