>it's something I struggle with. Different publications I have worked for as an editor handled it different ways. The OUP imprint followed the dictates of the Oxford Manual of Style - British spellings. The international fiction publisher used whatever version of English the writer worked in, and if they mixed it up, you made it consistent.
As a freelancer, I followed that angle. It was interesting to discover the varieties of English - Canadian and Australian English is different again.>