The correct colour wiring is normally available from specialist vehicle electrical suppliers likewise most terminals and connectors etc. In the UK many tractors for sale have a 'new' wiring loom but it is clear that it is an after-market one where the colours and terminals may be different. I made a loom to the pattern of the original for my 1974 MF165 and it worked perfectly. The important thing is to peg out the old one so that the new wires can be cut a little longer than necessary and taped every 6 to 8 inches to hold them together.
You will be able to find the relevant colours from the wiring diagram in a good workshop manual.
DavidP, South Wales