The first time I painted TH&B boxcars, I used a spray can of colour-match automotive paint from Canadian Tire. The colour was CTC #47-1949 AMC Mellow Yellow 1973-1975 E9. I don't have a photo of those cars, but I thought that it was a pretty good match.
The car Accurail boxcar shown below was done with Floquil - one part each of TTX Yellow and Railbox Yellow.
This freelanced caboose took inspiration from the TH&B's modern caboose scheme, although I'm not sure if the yellow is suitable for TH&B boxcars. It's SMP Accupaint AP-52 CP Action Yellow:
Wayne