CRW used to have a 2 tone option but stopped doing it. I would assume this is because they didn't make a very good job of it and in some cases was literally only one patch of paint somewhere on the gun.
I see they are offering some new service for England where by they send the gun in 2 halves but I cannot see how this is at all legal so wouldn't go ahead with that till you can get some confirmation that this is really OK.
Edit:
From UKARA website:
Bending the Law
Posted August 12th, 2009 by admin
We are getting reports of RiFs being imported in two halves and separate consignments and IFs coloured with removable paint, the new Boarder Services and Police are now taking an active interest in this and other attempted breaches of the spirit of the VCR Act and will be clamping down.
One wonders if there is some kind of death wish going on, we fought hard and long to get the
special defence for Airsoft yet idiots seem determined to throw it away.
Do not place an order with CRW like this.