I have 2 SNES mobo's one's the RGB-02 from 1995  and the other is the one with the sound daughterboard from 1990.  The 1995 mobo displays s-video in color.  The 1990 mobo displays s-video in black and white.  I've tried looking but haven't been able to find any documentation on if the chroma signal is output on the original SNES or is there a mod that needs to be done.

This guy found a broken trace. Others mention the pot near a cyrstal:




Have you looked at the board yet?

Does composite show black and white as well.

Look for the trimmer cap,its red and while the snes is on you need to adjust it,that might fix your problem.

Composite is in color.  The resolution is very blurry.  At first I thought it was the cable as one of the multi-system cables I have only displays PS2 and XBOX in S-Video.  But then I found a Nintendo S-video cable and it only works on the one mobo.  I'll check out the you tube vid.  Thanks.