FLAK 18s were the earliest model so panzer gray with a white whitewash for a winter camo. the scan is from the dragon FLAK36/37 with winter crew. H-1 is white, H-32 is field/panzer gray.
Yes, it all depends upon what time frame you want to depict. Up to early 1943, Panzer Gray would be in order for the base color. If in southern Russia, potentially the tropical colors used in Africa could be found as well. After February 1943 the three camo color scheme came into use, so the Gun could have been repainted with the Dark Yellow base and have the other two colors in a disruptive pattern under the winter white wash.