Its the owners that have the colours here as well.
Partnership form has to be completed for each horse....the first named partner in the syndicate is the partner who's colours the horse must run under.
The Dark blue/pink sets of colours is fine, Magnier was obviously the first named partner in that syndicate, presumably he had another horse in the race where he was also the first named partner so he must choose which one races in the second set. In that instance Tabor could not use his colours even though he has shares in his horses. It would have to be Magniers first or second colours or a change in cap etc.
I hear what you're saying, but still can't see how that fits with a horse running in alternative colours to those appearing on the racecard - i.e. Tabor's first colours, when on the racecard it's Magnier's second colours.
...Im getting a headache now. this seems to have hijacked the Derby thread. I'll need to go away and study some examples before having anything more that's sensible to contribute.