Dark Pale Tussock

This dark form Pale Tussock larva was hanging from a long thread off our apple tree in August. It was about 12 mm long and the usual pale green. I decided to keep it, and it subsequently moulted into a brown form. Initially the hairs were tinged strongly with pink but this was lost in the final instar. I've never seen one like this and neither MBGBI, Porter or Henwood & Lewington mention it, although lepiforum shows a pink-haired one.