Do unusual colors on pollen frames show that bees collect sugary substances with food coloring?

Not necessarily: even a color as unusual as blue appears in pollen in nature. The color of the pollen may even be different from the flower from which it comes. Rusty Burlew of honeybeesuite.com writes fascinating, researched articles on this sort of topic with illustrations. Here's one on blue pollen, possibly the most unusual color we beekeepers see in in our hives: https://www.honeybeesuite.com/bees-and-blue-beautiful-blue-blossoms-for-happy-honey-bees/#h-the-allure-of-blue-pollen