They mean here is a heart that is the colour _____. They don't have meaning. I use all the coloured hearts when I'm sending super gay messages to my super gay friends. We send each other rainbow heart messages whenever we're talking about gay shit.
Calendula is a plant. The flower is used to make medicine. Calendula flower is used to prevent muscle spasms, start menstrual periods, and reduce fever. It is also used for treating sore throat and mouth, menstrual cramps, cancer, and stomach and duodenal ulcers. Early research suggests that applying a specific gel (Estromineral Gel, Rottapharm-Madaus) that contains calendula, Lactobacillus sporogenes, isoflavones, and lactic acid to the vagina for 4 weeks reduces symptoms of vaginal atrophy such as vaginal itching, burning, dryness, and pain during intercourse. 2  Leg ulcers.
It should not be mistaken for common marigold, or Mexican marigold, both of which are in the genus Tagetes. Tagetes marigolds are popularly used in companion planting (to ward off bugs in the garden), and for combating nemadtodes in the soil. Calendula is for helping people.