John - There are two things to keep in mind here. One - the OD paint story fills a few pages .. and there are many variations of OD, depending on the year, the specifications, the factory, the vendor, the unit, right through to the CO and his ideas .. and even the country.
The best source for info on OD paint is here ..
http://www.olive-drab.com/od_mvg_odpaint.php
Either of the first two OD colors listed on the above site would be correct for a WW2 Cat.
Two - All paint dries to a darker shade than it appears in the can. Paint a little on a flat surface and let it dry, and see how it turns out.