The most common cultivar of raspberry is red, so why are most raspberry-flavored candies tinted blue?
The answer is two-fold: blue raspberries, though rare, do exist in nature. Blue-black in color, Rubus leucodermis, also known as the blue or whitebark raspberry, barely resembles the neon-blue hue that sweets manufacturers have adopted as the de facto hue for blue raspberry sweets. That said, the concept of a blue raspberry isn't completely fabricated.
Still, the question remains: why do candy manufacturers choose to tint raspberry sweets blue instead of red? Back in the '60s and '70s, ice pops like Otter Pops and Fla-Vor-Ice became popular. With four red flavors (strawberry, raspberry, cherry, and watermelon) in the mix, it was hard to differentiate them based on hue alone. While some colors were made deeper (cherry) or lighter (watermelon), raspberry became blue raspberry to make matters less complicated. Candy companies followed suit with a couple exceptions; notably, red Haribo Gold Bears are raspberry flavored!