David Mattingly - this wizard is available as a print you can buy through the artist's website! although the version on mattingly's website is much more blue-toned than this one.

interestingly, this is labeled as ""The Wizard In The Kitchen" by Barbara Hambly" on the website, although the book this is a cover for is indeed called "the time of the dark" as noted in this (presumably much older) scan. i wonder if this was a working title for the book! probably just a mistake (the book came out more than 40 years ago after all), but you never know.

it's interesting that the book cover version is more yellowy-looking than the blue one on mattingly's website and this old orangey scan! (i like this version best, personally.)