As I understand it from a spot of Googling this is an integrated TV/DVD player is it not?
On that basis there is probably not a lot you can do beyond the obvious like checking that you haven't accidentally turned down the colour control. It is possible that the TV uses separate picture settings for different sources so not beyond the realms of possibility that the TV could display Freeview in colour and the DVD in black and white.
And of course you are playing a colour film aren't you?
However it is probably more likely to be a failure of some section of the electronics internally. I can't really see that a dirty laser in the player would cause it to play in black and white. Much more likely to skip and break-up if it was a dirty laser. Cleaning the laser is probably the only action you can do easily to an integrated player and I doubt it is going to help in this instance.
Depending on how old it is it might be uneconomic to repair, unless it still has a warranty active on it.
