Beans
The Brits sure did use blue on some vehicles during the Desert Campaign, not just on the Stuart either. I remember reading that the Acadamy instructions say to do a two tone scheme but actual photo's of the depicted schemes, though black and white, clearly show 3 colours - the yellow and blue, but with green on top of the turret and cupola. I think that this is confirmrd in the Squadron 'In action" book on the Stuart/Stuart Honey, but just about any book I have seen on the stuart will have the pics of the vehicle.
See this pic for hints:
http://www.sunny-international.co.jp/syouhin/aca1399.htm.