Look through TDM Support_Gamemodes.cs, pretty sure I noticed a function Space Guy made that does it.
EDIT:
function RGBToHEX(%col) //In the form of R G B 0-1
{
%red = (getWord(%col,0)*255);
%r = getSubStr("0123456789ABCDEF",(%red - (%red % 16))/16,1) @ getSubStr("0123456789ABCDEF",(%red % 16),1);
%green = (getWord(%col,1)*255);
%g = getSubStr("0123456789ABCDEF",(%green - (%green % 16))/16,1) @ getSubStr("0123456789ABCDEF",(%green % 16),1);
%blue = (getWord(%col,2)*255);
%b = getSubStr("0123456789ABCDEF",(%blue - (%blue % 16))/16,1) @ getSubStr("0123456789ABCDEF",(%blue % 16),1);
return %r @ %g @ %b;
}