For years, I have come across anemones which have such vibrant, red/pink tentacles. They are rare to see and every time I take a picture of them, the color looks drab. I try all different settings, even without strobe but it always looks so dull yet to the naked eye, it glows. What am I doing wrong? Below is an example of an unprocessed picture of an anemone that to the naked eye, was so vibrant.

Natural red light does not exist at a certain depth. What you see here is a derivative of green fluorescent protein (GFP), a red-fluorescent protein found inside the anemone. The protein generates the red light from green or blue light. (The fluorescence is excited by light with a very specific, shorter wavelength). If the flash is too strong, it will overpower the fluorescent light. Without flash it should work. No idea why it doesn’t in your case. I photographed a similar looking anemone some years ago without problems.