The only real issue, if you want to get technical, is that OD has changed over the years. Humbrol 155 is very good for the modern color that I encountered in my active duty servcie in the 80s. But not spot of for the older Vietnam era OD shades (there were at least two different ones then) or the Korean era color, or the WWII colors. Basic rule- pick the one you like and run with it.