There is a lot a variables to that question, it also depends on weather the unit was in a combat unit or not and what time frame you want to represent. For SeaBee's the colors would be standard navy haze grey or if it was in a combat theater it would have been green. In the 60's it would have been Forest Green #24052 semi-gloss and after 1970 lusterless Forest Green #34079. For Air Force it could be Strata Blue #15045 or if in a combat theater it would have also been Forest Green #24052 and again after 1970 it would been Forest Green #34079.
Now the next part, I have never seen an original picture of a M725 in any markings other than the Army, but that doesn't mean that they are not out there. Just that if they did transfer to other branches, they were if far less numbers than what the Army operated. The Air Force and Navy really had no need for a combat capable field ambulances like the Army since most of their operation where on or around bases which usually used civilian ambulances.