I'm wondering what kind of grey did germans use on their Hanomags, Marders, etc on eastern front, was that the same dark grey that was used 'till '43 when dark yellow came in use?

Yup it was...

yes the germans used panzer grey on the easten front, russia.
and they used panzer grey on the westen front, that is when they fought us,
they used the grey color till feb of 43.
then after feb 43 they went to the dark yellow.

Thank you, on more question, is the Hanomag's "interior" painted with the same color?

Yup, one colour inside and out.

If you're worried about the finished model being too monotone, then don't. Because the colour of the seats, internal fittings, driver's instruments, the floor of the SdKfz 251 (scuff marks, exposed metal and slight rust), quite a bit of 'muck', maybe a few loosed MG42/34 shell cases rolling around and the crew's gear will add variation in colours.

Hi there !

As mentioned before, panzergrau is alright as a primer. Secondary color could have been MUD. Yeah, really ! It was applied with brushes. In '42 stey started using green as a secondary color to brake up the shape of their vehicles. Some nice reference pictures in "panzer colours" vol. 1-3. There's a picture of a Panzer III in original grey, additional green airbrushed stripes and over that large stripes areas of dark yellow. Looks fantastic.

CU

Frank