Dopamine is triggered by the expectation of a reward. Flowers were a huge reward signal in the world our brain evolved in because they marked the coming of abundance after a hungry winter. Today we have enough to eat all year round so we don’t consciously link flowers with food. But the blossoming of a flower triggers the sense that something special is coming because it triggers dopamine.
Bright colors signaled valuable nutrition for our hunter-gather ancestors. They balanced their diet by scanning for spots of color. They didn’t do it because they knew the chemistry; they did it because dopamine made them feel good. Today, color and variety make you feel good and get your attention even though you can get the nutrition in other ways.