Heck, the orange was probably just the closest they could come to brown using the limited color palette of early comics. Just like Batman's "blue" cape was originally supposed to be a black cape with blue used to represent its highlights (much like characters meant to be black-haired were often shown with blue hair).
Then again, Kirby originally intended the Thing to be scaly, not rocky. The rocky texture came from later artists' interpretations. So maybe he was meant to be orange.
Then again, Kirby originally intended the Thing to be scaly, not rocky. The rocky texture came from later artists' interpretations. So maybe he was meant to be orange.