Ians right, Olive Drab does fade/weather very quickly, especialy in the conditions you're depicting there Don.
I have restored many vehicles over the years and know how some colours fade more than others. When I hauled my 1942 jeep out of it's hiding place in an old shed I found a lot of original paint. Where it had been exposed to the elements it looked almost yellow! but behind brackets etc it was still the original O.D. (Don't start a debate on the correct shade of o.d. as it will go on for ever!!) I had the use of my own paint mixing scheme and found the original P.P.G. formula from 1942 for Olive Drab and found that there is no green tinter in it..just Blue black, orange, yellow, white. The blue black mixed with the yellow gives it its green colour. see, yer larn sumtin' evry day!!
Jeff