US vehicles - I use humbrol enamel #159 khaki drab and put a wash of tamiya acrylic XF51 or red brown over it with some dry brushing of dark green if necessary.
German vehicles - seats normally leather in the trucks so a brown leather look is best with dry brushing and washes to suit.
As to texture on seats if the plastic is too smooth I use a course sandpaper and "texture" it before painting.