This is an interesting speed painting video, in a 2-color scheme of Vallejo Model Air:
  1. Parched Grass 70.610 + Dark Yellow 71.025 (50% - 50%) mixed with Airbrush Thinner on the base, and then...
  2. Dark Yellow 71.025, thinned with Airbrush Thinner

There leaves just enough variation between #1's base color, and #2's spot color.

I might try this for my first go at T-64's.