If you like purple, forget on trend & have it. I adore purple, have a light oak & white gloss handles kitchen going in next week with a deep plum purple glass splashback. I couldn't be less worried about how unfashionable it will be in a year or so because it will make my heart sing every time I see it.
I have an olive green glass one above my hob. Absolutely love it. It tones in with the decor and is the first thing people comment on when they come into the kitchen! Glass is really easy to keep clean too.
As you already have colour elsewhere keep the backsplash fairy neutral. If you want colour go for something that picks up on the oak. Purple will date your kitchen. See what I've done with some of my kitchens www.designandconker.co.uk