It doesn't specifically call out the colour as something they verify in the VRT inspection. However it does state that if the details,don't match the documentation then the car will not be registered:

http://www.ncts.ie/vq4.html

It would take 2-4 weeks on the UK side to register the colour change with the DVLA:

http://www.findlaw.co.uk/law/motoring/vehicle_registration/9951.html

If it were me I'd be doing the colour change on the UK side.