Red and black currants are pretty popular in Europe, I'm given to understand. Rhubarb is delightful, though!

I had to look up billberries, and they are intriguing! Adding them to the pile of Blue Fruit Options. (I think cassowary fruit is probably my favorite conceptually of the ones I know about, but I don't anticipate getting to taste it any time soon.) I also kinda think of Vipereon as a bit more of a blue-ish green/teal than gray-green? IDK.