OK, I just called UK Customer Services, who in turn have just called sales for me. I can confirm that based on what they said, the Colour MFD is standard on the GTI, and optional on the GT spec down.
I'm going into my dealer to finalise the finance to today, so will confirm for sure with them then and see whether or not I need to keep it on the order.
Update: OK, just got back from finalising the numbers, and we have decided to just leave the option selected. If it's not standard, the current price will stand. If it is, I'll just get £135 deducted. Simples!