Some mid-2000s JVC D-Series and I'Art televisions have a firmware bug where suddenly color will only be present on component video. My I'Art went to black & white on composite, S-Video, and even RF. It's as if it were expecting two more color sources on every other input. This happened the first time I connected an XBOX 360 to it.
If this happens to you, you'll need to access the service menu. With a compatible JVC remote, press
SLEEP TIMER, then simultanously press
DISPLAY + VIDEO STATUS.
From the service menu, select
1.V/C(S). The option we're looking for is
APC CLK, although the number it appears under can vary by model. It was S47 on my AV-27F704. The setting here should be 1. If it's already 1, try toggling it back and forth. This has been a confirmed resolution for multiple JVC owners in The CRT Collective on Facebook.
Posting this with the verbose title as I was not able to Google my way through this when it happened to me. I tried r/crtgaming and The CRT Collective with no luck at first, but eventually the community on Facebook came through. Hopefully this information finds who needs it.