First of all check the connections between your DVD Player and the TV.
If you are using SCART leads, make sure the plugs at each end are firmly placed in the sockets. It is a common fault on SCART connectors.
I use SVHS connections for my DVD Player, but obviously the DVD Player and TV have to have this facility. If a connection gets knocked or otherwise disturbed, the picture can still be there, but you will have lost the colour.
If this doesn't work, let me know by posting an answer to this question.
Good luck