What is the difference between the white and the yellow markings used on D-Day vehicles. Why was there two colors?

Because they had two colors of paint available? (sorry, couldn't resist)

They were probably both used. It is nearly impossible to tell the difference between white and yellow from black and white photos. Adding to the confusion, early tanks were marked in yellow and blue drab -- some were painted over in white while others were left as-is.

You might want to do a search on Missing Links -- I know the subject has come up a few times. Also, check out Steve Zaloga's D-Day M4A1 in the gallery: http://www.missing-lynx.com/gallery/usa/m4a1_zaloga.htm He did the shipping stencils in white on this one.

It might also help you with your wading stack question!

One note -- I usually don't suggest using other people's models as reference, but in the case of Mr. Zaloga's stuff, I make an exception to policy.

I'm on it Bob, thanks.

I found the full article Steve Z. wrote in MM on that D-Day Sherman. Volume 33, No. 6, page 32. Actually, some else found it for me.
It's been a life saver!

As far as the colors, I just was not sure if they were used seperate ADs or battalions or whatever. I think I'll stick with white.