The appalling story of neglect surrounding this movie is taken up by Halliwell (emphasis mine):

‘Colour is in fact one reason for its long disappearance.  Dupes being expensive, only one master negative was kept.  When the story was remade, more or less, in 1953 as House of Wax, an enterprising British publicist requested a copy of the original for a comparison showing to the press.  He was sent the original; never used it, and instead of sending it back had it destroyed to avoid storage and shipping costs.’

MVD video recently released a truly awful print on a double DVD, coupled with a slightly better version of Island of Lost Souls.  I guess we should be thankful that any print survives but it would seem no restoration has ever been undertaken of the film, but this is one film that is crying out for the Criterion treatment.