Code:
<?xml version="1.0" encoding="utf-8"?>
<GraphicsConfig>
<GUIColour>
<Default>
<LocalisationName>Standard</LocalisationName>
<MatrixRed> 0.1, 0.1, 1 </MatrixRed>
<MatrixGreen> 0.5, 1, 0.5 </MatrixGreen>
<MatrixBlue> 1, 0.5, 0.1 </MatrixBlue>
</Default>
</GUIColour>
</GraphicsConfig>

which I use (mostly a light/bright blue HUD).