Olive Drab vs. Khaki

Military khaki has a slight greenish hue, sometimes called pea-green khaki and is very often refered to as OD#3

OD's range from 1-33/34

Around this time frame 35-80's most every manufacturer was vat dying OD colors it's quick it's easy it's cheap ... But... It wicks into the fiber and because of this you get fading and color variations ... Many color variations ... 

How long the fiber was in the vat ... How dirty is the vat... How old is the dye ... Is it cold dyed or hot vat dyed ... Is the vat continually mixed or does color settling happen because it's not ... So many variables I don't even think I hit a third lol

In comparison today most quality fabrics are solution dyed where as the fibers are colored before hand ... Synthetics the color is added before the fiber is even extruded... That's why these keep their color much longer without fading 

One OD could look like a 3 and somebody's 3 can look like a dirty 5 as well as somebody's #5 is in fact more so a number 3 or 4

Today when you buy Khaki it is like the far left jacket ... it is not an OD#3 ... it is Tan