Region 1 DVD plays in black & white
 

I recently changed my Region 2 DVD player (Sony DAV-DAZ100) to a multi-region one, and bought a region 1 DVD to test it out.
It does play, but it's in black & white. My region 2 DVDs still play in colour.
Does anybody know why this might be & how to fix it?

The rgn 1 disc is probably NTSC.

Does your player have an NTSC/PAL selector?

This probably doesn't help, but some years ago I was living in Europe and had a multiformat VCR. When a friend from America sent me a region 1 (ntsc) VHS tape, it would play back in b&w. Turns out that for me to get colour playback, I had to connect the VCR to the television set via SCART, not just RCA or coaxial. Both were typically an option in European TV/VCR connections. Anyways, that may not apply to your situation, but that was my experience.