Trying to track down a story about Joni Mitchell and David Bowie

There’s an old anecdote–I think it was from the early 90s–about David Bowie and Joni Mitchell. Both were painters as well as musicians, and there was some kind of event celebrating musicians who distinguished themselves in other fields of endeavor, called “Twice Blessed.” Anyway, they were both there, and Bowie said something like “I’ve got a tip for you: Add a little white to your paints.” And Mitchell said “Yeah, to lighten it, everybody knows that!” (It actually makes color paint more opaque, but that’s neither here nor there). I remember this being from an interview with Joni Mitchell, maybe 25-30 years ago, and I want to nail down the details. Does this ring any bells with anybody?