"Blue Raspberry" as the name of something isn't really too far fetched.

Most raspberries turn from green to red to purplish as they ripen, but my grandpa had a couple of bushes of a variety that almost completely skipped the red and went pretty much straight to a true blue, and the "squeezins" actually were "just plain blue."

Since the flavor wasn't noticeably different than the red/purple ones, a "blue raspberry flavor" doesn't tell much though.

The "blue" variety grandpa grew might have had a more distinctive flavor when grown in a better - or at least different - climate. Kansas has pretty fair soil, I guess; but the climate isn't necessarily all that wonderful for a lot of plant life that grows more easily "around the corner and down the road a way."

John