I was searching too and i found

set(info_pan,LIGHT); // modulate all panel bitmaps with the given color
vec_set(info_pan.blue,vector(0,0,255)); // red color
Change "info_pan" to name of your panel.
I am not sure if is the right way, but it works.
I know is boring but sometimes is better to make a search on 3DGS Manual.
Lesson of day

I hope it helps