Acanthophora spicifera (Spiny Algae)
Acanthophora spicifera(Spiny Algae as it is commonly called) is one of those red algae that are highly variable in color. Sometimes it is red, others yellow and sometimes brown and even green or purple. Not just species variations, the same plant can make this transition in a short time. It has to do with light intensity and wavelength. The brighter the light the paler the color usually.The bluer the light, the darker the shade.
Fiddling with color by shading the plant can be fun for the collector who enjoys a hobby challenge. With the right skill they may be able to bring out the purple in this seaweed. We often see it as a lavender color in the wild, but haven't been able to duplicate it ourselves.
If you would like to learn more about macro coloring we have a brief article here:
Towards the bottom you should find some info that should be helpful.