Build-Up of US Army Vehicles Before D-Day

Castletown Road Slipway, Portland, Dorset (England), 5 June 1944. Trucks and Willys MB jeeps which will carry men and supplies of the U.S. 32nd Field Artillery Regiment / 1st Infantry Division "The Big Red One" to the front lines of the invasion in Normandy on D-Day are loaded onto an American Landing Craft. The Divisional HQ jeep at right (with Divisional HQ tactical insignia in the bumper: black star on dark yellow circle; 1-X: indication of the Division Headquarters; Star in center bumper; HQ-19: 19th vehicle of the Division Headquarters; and Barcode with five-digit number of the DivHQ) has an 15'x15' vehicle camouflage net (this type of net with interwoven twine came in different sizes) above the white star on a yellow background marking. The yellowy green (or greeny yellow) background between star and circle was a kind of gas detecting paint that was supposed to change colour during a chemical attack. Presumably these jeeps are an example of the stuff. Might also be worth noting that a yellow or white star in black and white photos would show up the same tone. Closer analysis of even quite familiar black and white pictures recently seems to be turning up even camo schemes that have been almost lost in the monochrome process. In the dust and confusion of the battles in the North Africa previously, the US star could be mistaken for a German Cross at long range (greater then 1000 yards). Tankers and armored units began painting out the stars to avoid becoming a casualty of ‘friendly fire’. The addition of the circle around the star helped to resolve this problem, though some of the more experienced units (like the 2nd Armored) stayed with the painted out stars until the Normandy landings. There they painted the vehicle number on the sides of the turret in yellow. This was painted out by D-Day + 14. After Normandy several armored divisions were sent into Europe but kept their stateside markings, except the bar, and that is why one sees so many variations in pictures.

Source :
http://historylink101.com/ww2_color/WorldWarIIAmphibiousUnit3/PICT0442.html
http://www.usmilitariaforum.com/forums/index.php?/topic/57160-the-liberator-collection/page-18
http://ww2talk.com/forums/topic/6397-yellow-circles-white-stars/