Arnold has coloured his hair for a long time but his hair is clearly his own. His hairline has been consistent throughout all his life from a very young age (how many thousands of shots of him are there from his mid-teens on) and is mildly receding now as he enters old age. It is a classic high germanic hairline-a third of men never lose their hair it's not like he is a genetic freak keeping most of it. And that link with a few photos did not show anything at all unnatural.
Hollywood stars are still pretty easy to spot when they do have rugs even with all their money + there are earlier age photos that clearly show the hairline difference or obvious plugs (stallone, nic cage, travolta, brendan fraser etc.)-neither is the case with arnold. He's still got most of his hair-a lot of people do.
