The problem with your question is that there is no unambiguous way to define a "number of colours." Not only is there a visible spectrum with infinitely many distinct wavelengths, each in principle corresponding to a different colour, those wavelengths can be combined in infinitely many ways to form composite colours.

I think it would be reasonable to group colours by the categories a language uses to group them.

English, for example, has categories like "red, orange, yellow, green, blue, purple, pink, white, grey, black"

Colours would fall into one of these categories and two different colours that fall into the same category would be considered "the same colour" for the purpose of this discussion.

There will always be colours in-between categories that are hard to categorize.

What wavelengths can bioluminescence produce?
And which combinations of wavelengths can be produced together by biological processes?

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Why not just list the wave length ranges if they are known?

Let's divide your question into two parts: what colors can bioluminescence produce and what colors can humans see?

Since I'm more knowledgeable about humans, we will start there.

Let's start with a definition of light. Light is electromagnetic radiation that people can see. People can see radiation from about 400 to 700 nanometers in wavelength.

Most people have three types of color sensors in their eyes, commonly called cones. We have sensors for red, green, and blue light. When our cones sense light they send signals to the visual cortex part of the brain. Through the magic of neural processing, light signals are turned into a great many different colors. People are able to distinguish literally millions of colors as long as those colors are displayed as large uniform patches. When the color patches are small, we can't distinguish colors nearly as well. When it gets dark, we lose the ability to distinguish colors and everything fades toward grey or black.

Here's some of our neural magic: carefully adding red, green, and blue lights together makes white. Red and blue light make magenta, that makes sense. But red and green lights make yellow.

You wrote that bioluminesce can produce blue, green, and red light. If this light can be uniformly mixed over say a couple of square inches, then bioluminesce could produce millions of colors and indeed every color visible by people.

My little discourse talked about additive color mixing or what happens when you mix lights of different colors together as occurs on a computer monitor. There is also a process known as subtractive color mixing when pigments are mixed together as in printing or painting. Each pigment subtracts some wavelengths of light from what we see. In the subtractive process, people typically use 4 primaries: cyan, magenta, yellow, and black. Strictly speaking, black as a primary is redundant but it is cheaper to use black ink than a muddy mix of the other primaries to create black.

Those categories are not unambiguous either.

Bioluminescence produces light at all wavelengths of the visible spectrum.

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> couldn't any color be replicated?

Pretty much, yes. Learning how to design modified versions of fluorescent proteins took some time + quite a bit of research, but people have gotten pretty good at it.

you may find this interesting, these are a range of engineered fluorescent proteins available over 20 years ago. Many more are available now, AFAIK the entire visual spectrum is available for purchase now.

https://www.researchgate.net/profile/Olga-Markova-2/publication/299382987/figure/fig1/AS:650036895576076@1531992281254/Palette-of-fluorescent-proteins-Engineered-fluorescent-proteins-cover-the-full-visible.png

> are those colors just the best evolutionary fit for the environment?

Again, pretty much yes. There's no technical reason why certain colors of fluorescent protein couldn't have evolved naturally, so the fact that they didn't suggests that for whatever reason they aren't advantageous.

I am not a biologist, so take my answer with a grain of salt. I wouldn't respond except that your post is getting stale and I don't see anyone addressing the core question. Mods feel free to Dunning-Krueger my comment into oblivion if somebody else gives a more cogent answer to OP.

The question of "can" is easy to answer: Given funding, we can find some biological molecule that fluoresces at any wavelength you want between about 350nm and a few thousand nm. (human sight is about 400 - 700nm) Below about 350 is hard because it takes a lot of energy to generate.

The question of evolutionary fitness is more interesting. Evolutionary adaptation does not "seek new solutions". Rather, some random adaptation is evolved, and if it is advantageous it has a chance to become widespread. The advantage of bioluminescence is beyond my training, but I assume (perhaps wrongly) that it provides some competitive advantage in hunting/attracting mates/whatever.

Two factors are worth considering now:

1. How likely is it that an organism mutate to produce a bioluminescent protein at wavelength "X".

2. How advantageous / disadvantageous is that mutation?

To point (1) it is likely that some luminescent proteins are just one or two mutations away from some other protein that is common. These mutations are likely to occur more frequently than others, and are therefore more likely to catch hold if there is some competitive advantage to bioluminescence.

To point (2) if a luminescent protein is easy to achieve by mutation but is very energy intensive or poisonous or whatever, it is less likely to produce a net competitive advantage.

In some population, if two different mutations can occur, one being a low-cost protein at wavelength "X" and the other being a high-cost protein at wavelength "Y" I would expect the former to take hold in the population. And once the capability to luminesce at wavelength "X" is evolved, it becomes much less likely that a capability to luminesce at wavelength "Y" subsequently evolve. The organism already has a means of luring food/attracting mates/whatever. A mutation that produces another (more costly) method is a competitive disadvantage in most scenarios, unless there's a "Red Queen" situation where the organism is under a lot of pressure to evolve new capabilities due to competing evolution of a predator or similar.

Why blue-green for aquatic and red-yellow for terrestrial? The attenuation of light in sea water is wavelength dependent. Blue-Green propagates better than red or blue. That color is called "Aqua" for a reason. UV is rapidly attenuated. Presumably, then, a mutation for bioluminescence in the UV or IR provides little or no benefit. For terrestrial, red and infrared propagate just fine through air and are less energy-costly than blue or green. I have no idea if there's a lot of infrared bioluminescence, but I wouldn't be surprised.

Thanks for the non bio take. Heard that Bio is applied Chem which is applied Physics (least on the smallish scale).

Was overall curious if we would ever replicate bioluminescence proteins to make something multi color.

There are chromatophore cells (especially for Cephalopods) that can do a variety of colors as well.