I've found that the Dupli-Color Alpine Green is quite dark for the 1970s Detroit Diesels. What I use is Testors Model Master Grun RLM 62. Here it is an a 1970 American-LaFrance Series 1000:
For Cummins Beige, again the Dupli-Color seems too dark (almost Brown), so what I use is Tamiya Deck Tan XF55. Here it is an a 1980 Kenworth W900:
For Detroit Diesel Series60 Blue, I use Tamiya Medium Blue XF18. (Sorry, no pics of that yet!) It's a pretty close match.