The larva of Daphnis nerii has been posted in various threads on several occasions. However, this is the rarer (I believe) brown form. Unfortunately, the cat died of a viral infection before pupation.
The species was identified for me by Dr. Ian Kitching of the British Museum of Natural History,
I think that's the colour they change to right before pupation.
The last time i had one, it turned from green to bright orange and brown, just like urs.
Thanks Aaron. However, this larva was nowhere near pre-pupal stage. According to Dr. Kitching, this is a known, but rarish, colour variation, which is kept throughout its larval stage. The final moth, however, is quite normal.