welcome Mark.
Why trade up to the R50? Whereabouts are you? The RNS510 map screen is colour. If you're referring to the Multi-function display between the tach and the speedometer, I'm thinking there's been a problem in the past and a non-colour MFD has been installed.
Really need more detailed information in respect to what you are referring to.
Don't be offended....but I'm surprised you've put the deposit down before coming here to ask about known issues. Cart. before. the. horse?