Greif was originally Dark Gray. The desert color used is RAL 8000 which was sprayed over 2/3 of the vehicle. The remaining 1/3 was supposed to be RAL 7008, however with shortages of paint, it appears the 7008 was never applied.
RAL 8000 is in actuallity quite a dark color. That was the plan, the darker color wouldn't look so dark in the intense sunlight and allow better concealment.
Google "Bovington Tiger" for a good color reference of RAL 8000/7008. Tamiya Desert Yellow is not correct out of the bottle. If used out of the bottle as RAL 8000, don't lighten it at all. It can be used though, as it is the closest unaltered Tamiya color.
Other manufacturers offer more correct RAL shades.
I only use Tamiya mixes, based on Starmer's research, for my RAL Tropen colors.