Plants with high beta-carotene and zeaxanthin help enhance a hermit crabs color. I became fascinated with the burning bush that my husband planted one year. The green leaves that you see in spring and summer contain chlorophyll. In the fall, when the chlorophyll breaks down (green pigment fades away) a brilliant, almost florescent red emerges. Leaves that turn yellow contain xanthophyll. Orange indicates carotene. Red and purple indicate anthocyanin. In the world of hermit crab enthusiasts, carotene equals bright crabs. The effects of the other two substances are unknown to me, but it seems that they should have related properties. Several of my food trials will focus on plants with brilliant fall colors.
Astaxanthin and tannin are also color enhancing.
To boost your hermit crabs color, try adding these to their diet:
Spirulina (a sort of seaweed)
Cilantro (aka coriander) Parsley