Thanks Mike & Marc,
The SNR on the R channel was about 4 times the SNR on G&B - not a lot of signal at all.
I've been looking at a pro-am collaboration image from the ESO - there's actually a bit of blue in the middle of the 3 pads of the paw.
Link I did see some vague colour during processing, but thought it was noise and tried to minimise it. Might have to have another go with some more G&B subs...
DT