First, it should be easy to find out which paint was used on the prototype. That can be found out on certain forums.....like this one.
Paint bottles usually say....UP Armour Yellow, SF Blue, CP action red, NS black...etc....
Now you will find, for example, that paint colors vary from paint mfg to mfg....example would be scalecoat CP action red and Floquil CP action red....they are noticibly different.
Now, pertaining to which colors belong on which locomotives, pictures are your friend.
Which scheme are you thinking about?
David