If you cut out the DVD recorder and go direct from the YouView box to the TV using SCART do you get a colour picture?
If so (and I'll assume so for now) then it looks like a problem with the signal format output from the YouView box not matching that expected by the DVD recorder's SCART.
Also, is this problem just in "pass through" mode - you're not actually recording anything on the ES10, you're just passing the YouView signal through it to the TV?
Panasonic talk about this kind of thing here. The YouView box will be sending output in Composite (Video) and RGB format I think. The video recorder which works OK will be sending Composite (Video) only probably.
Can you take a look at the settings for the SCART socket on the DVD Recorder (AV1 or AV2 if I remember the ES10 correctly) and experiment with different formats? Switching between Composite / RGB / SVideo to see if a combination gives a colour picture. I'd doubt that SVideo would be the right setting but give them all a try and see if any sort it out!
Could it be encryption? Possible I suppose but I'd expect the DVD recorder to just refuse to record a macrovison encoded signal and I don't think the YouView box will encrypt the signal from live TV - it may well do if you try to transfer non-live TV to the DVD recorder.
Hope that gives some ideas of settings to play with at the very least. Good luck!