Open the file default.ide from the data directory with Notepad and replace the line 167 with this:
167,	coach,	coach,	car,	COACH,	COACH,	coach,	ignore,	10,	7,	0,	255,	1.100000

For changing the colors, open the file carcols.dat with notepad and replace the coach line with this:
coach, 56,71, 75,71, 13,71, 44,27, 67,71, 55,52, 21,26, 74,15