From what I understand (and maybe I'm wrong), it wasn't uncommon for camo jobs done on German armored vehicles to be done in the field (especially towards the end of the war). Some factories would just put on a base coat of paint and ship them off. German paint that was issued to the field was designed to be mixed/thinned with basically any liquid - from water to diesel fuel - one reason that there is such a variation of color on german armor. Painting your halftrack just dark yellow is perfectly fine - I'm sure there were many just like that where the factory delivered it that color, and the crew didn't get around to camo-ing it up, or didn't feel that it needed camoflauge.
I also want to add that the painting done by crewmen in the field was usually done very quickly and therefore usually looks very sloppy. The whitewash you were talking about is usually done with handbrushes by the crew. If you are thinking about doing this, do it by hand (like the crew would have done) and don't worry about brushstrokes showing or about getting the whitewash in every crack and place on the vehicle. Look at period photos whitewashed vehicles - sometimes the whitewash isn't even a solid coat. It's good to do some drybrushing over the whitewash to show wear also - the whitewash was usually a water-based "wash" and would even wash off in heavy rain.
Speaking of sloppy paint jobs, there is a photo of a newly caputred Tiger I that I have seen in color (wish I had it to attach and show you) that illustrates exactly what I am talking about . It has a 3 color scheme, and the paint job looks like crap! Lots of runs everywhere, etc. - nothing like the pretty lines we like to put on our models. Hope this helps!