Ok I'll try and help.
Tamiya buff is fine.
For the oils I would mix the following.
For the base mix, Titanium white then add small amounts of yellow ochre and burnt umber.
Shade add a touch more burnt umber to the base mix.
Highlights add a touch more white to the base mixture.
Looking at the picture it seems touches(very tiny) of mars orange have been added after the basic highlight and shading stage.
Hope this is of some help.
All the best.
Ralph.