Sure it's not a MONOCHROME version of the Mk4 as used in the Business Nav installation?

What is the part code on the Nav Computer? IIRC if it ends in M it's mono, if it ends in C it's a colour one. It can be recoded though using Navcoder and an i-bus interface.

Post up the part number and model number and Kiwijochen will be able to help you.