well, i read the english version and it sounded like he was pretty red... he was just covered in his gold coins and jewelry so much that gold rolled off of him, i think.
um... here's a copied and pasted excerpt from the book i read:
" There he lay, a vast red-golden dragon, fast asleep; thrumming came from his jaws and nostrils, and wisps of smoke, but his fires were low in slumber. Beneath him, under all his limbs and his huge coiled tail, and about him on all sides stretching away across the unseen floors, lay countless piles of precious things, gold wrought and unwrought, gems and jewels, and silver red-stained in the ruddy light. Smaug lay, with wings folded like an immeasurable bat, turned partly on one side, so that the hobbit could see his underparts and his long pale belly crusted with gems and fragments of gold from his long lying on his costly bed."
so, i guess he was red-golden, lol i've always pictured him as a red dragon that was bathed in golden light