UL 845, the standard for MCCs, does not address conductor colors at all, in fact the word "color" is not in the document at all, nor is the word "white" (red is in there referring to barriers).
NFPA 79 is the standard for "industrial machinery" and says the following:
14.2.3 Identification of the Grounded Circuit Conductor.
14.2.3.1 Where an ac circuit includes a grounded conductor, this conductor shall be WHITE, GRAY, or three continuous
WHITE stripes on other than GREEN, BLUE, ORANGE, or YELLOW insulation along its entire length.
Then later:
14.2.4.3 The use of other colors for the purpose of identification shall be as follows:
(1) BLACK for ungrounded line, load, and control conductors at line voltage
(2) RED for ungrounded ac control conductors at less than line voltage
(3) BLUE for ungrounded dc control conductors
Basically, it could go either way, you could say that if you have a grounded secondary on a CPT, the wire should be white, or you could say that because it is a control circuit at less than line voltage, it should be red, because it is not grounded until it is connected to the grounding stud near the control transformer. But when the actual starter COMPONENT was made, how do they know if the control circuit is going to be grounded on one side or not? They don't, even on 120V control circuits, it's perfectly acceptable to NOT ground one side of the CPT. It's the accepted CONVENTION, but is not DICTATED; you can have a "floating" 120V system if you want to. They don't ground 120V circuits in the Navy for example (I've hired Navy trained electricians, it's a tough habit to break them of). So they leave it red at the factory, and history has dictated it somewhat as well.
Many moons ago, it used to be commonplace to use "line voltage coils" on motor starters, i.e. control power for the starter was tapped off of the power lines with 2 small fuses, so it had 480V coils and 480V running to the pilot devices on the door. When I started out in the 70s MOST of the starters I wired up in the steel mill were done this way. In that case, there was no "neutral" circuit at all, just two lines of 480V, nothing was grounded. So when building the motor starter in the factory, about half of them were like this, the other half used 120V coils. But to make two different versions in the factory was expensive, i.e. one with a white wire on the grounded side of a 120V coil, and one with all red for a line voltage coil. So the solution was to just make them all with red wires regardless of the coil voltage, so you could make only one version and swap out the coils themselves just before shipping them. Whether or not one side of the control circuit was grounded or not was a detail for the installer, and nobody was going to go out and change the little piece of red wire on the factory assembly. If you ran your OWN 120V (aka "separate control) from a panel into the MCC bucket, you would run white wire out TO the bucket terminal block, but on the factory side, it would be red. So how it works now is that if you are buying a "standard" or "quick-ship" MCC that comes with the factory bare minimum control wiring, everything will be red in the control circuit. If you buy an "Engineered" MCC where each bucket has special custom 120V control wiring
and there is a user spec calling for grounded conductors to be white, you get white, up TO the motor starter OL contact terminal. The other side of that, from the coil to the OL contact, may still be red.
