1. There are more than 1 color or "Olive Drab". Just like there are many different other colors like Khaki.
and
2. When reading about different colors and combinations and how they are made. Olive Drab is a mix of Black and Yellow. Shocker! at least to me.
I too do not have an airbrush yet so I share our limitations with painting ability.
What I have learned about when researching painting armor models and such is All about Paint Filters. Filters are available in Enamel and Arylic. They are used by alot of the big modeler content contributors to tint or alter the paint that you are looking to change to the way you want it to look. You can also combine different filters. Big modelers also do things like pre and post shading as well as blending.
Remember it's Filters, not Washes they are 2 different things used for different purposes.
I hope this helped because I can completely relate to your issue.
Chef
PS AK, Ammo/Mig make great great filter products that I use.
PPS here are 2 different Heng LongTanks that retain the Stock out of the box paint just adjusted with different paint Filters. And other stuff too but the Filter alone makes a noticable difference as compared to the brand new out of the box paint:
Good morning,
I would like to do the same? it looks like a real painting done in aero. In my case, I don't dare touch the Sherman anymore, otherwise I'll spoil it 
but overall yes, except maybe some paint references?
