Hi Marengo, well done! Yes, his body was covered with the coat he wore at Marengo. Now from 3 French historical references the color I have is blue with gold embroidery .
Hi Grognard, I seem to be partially right.
Of interest was that british Captain J. W. Crossley later cut a piece of the collar as a souvenir. The remainder of the cloak was believed to be burnt in a fire in London in 1825, and this is believed to be the only surviving fragment. It was of wool cloth, and as you said blue embroidered with gold thread. A picture of the precious fragment can be seen on the "Treasures of Napoleon" website. Also of interest (but may contain some myth) was that after Napoleon's death was announced, Madame Tussaud's displayed a wax death bed scene and they used the Marengo cloak (which had been willed to Napoleon’s son) to cover the corpse, and early one morning Jacques Tussaud found the Duke of Wellington gazing on the wax body of his great enemy.