It's likely the output connection of the DVD is not set to match the AV input of the TV.
If the TV is also Panasonic and the picture suddenly went black & white,..
Simply select TV/AV on Television handset, then "** while coloured AV options are displayed on screen **", press the GREEN Fastext Button, it toggles the TV connection between "AV2 or AV2S", one of the settings should restore the colour.
Otherwise...
In the DVD-RV31 Set-Up Menu, look under Connection/AV1 Output.
Options in this Menu are likely to be; Video, S-Video or RGB.
ie. if the TV is also Panasonic, it's connections are...
AV1 - Video or RGB
AV2 or AV2S - Video or S-Video (toggles as described above).
AV3 - Video
AV4 - Video or RGB
The setting you choose in the DVD set up menu, must match the input you've chosen on the TV.
Use a good quality fully screened scart lead for the connection.
Cobweb, December 2004