The London Lounge

I understand that the classic colour for the military-inspired trenchcoat is tan, khaki or beige (light colours).

Is there a classic colour the trenchcoat's cousin - the cotton raincoat with flyfront, shirt collar, and Raglan shoulders? I plan to use it over business suits generally, and ocassionally over casual jumpers when business travel stretches over weekends.

From everything I have seen and read on the subject, the color of the military-inspired and the flyfront collar are both generally the same. With the exception of the flyfront collar coat commonly seen in navy.