Jesuis,
As I understand it the proposed definition of mass which allows photons to be said to have mass, relies upon movement. The photon must be moving or the calculation fails to produce mass. So once the light reaches the singularity, the mass would vanish. Keep in mind that I may be misunderstanding the concept.
As far as a black hole comprised completely of light, one must remember how a black hole forms. They start as a collapsed star. So even if one consumed only light, it would still have the mass of an entire star at its singularity. By studying the light from a star, we can discover that even in just the visible spectrum (4000 to 7000 angstroms), there are indications of at least 67 elements. The most abundant in our sun are seen to be helium, hydrogen, carbon, iron, oxygen, nitrogen, silicon, magnesium, neon and sulfur. Our sun, of course is a second generation star (as are all other stars we've analyzed). A first generation star would contain little other than hydrogen and helium.
As far as converting mass into light, I'm clueless. I don't know if this is theoretically plausible or not.
For the most part, when we see energy emitted from a black hole, it's in the form of electromagnetic signals such as radio and x-ray. The energy doesn't actually emanate from the hole itself (inboard of the event horizon), however, it's generated by the rapid acceleration of particles as they rush to the event horizon.
In regard to the color spectra of light, black is the absence of light but light can appear any color. It's only when you mix the entire scope of the visible wave lengths that we perceive white light. If those wave lengths are scattered and diffused, such as occurs in Earth's atmosphere, the color we perceive will depend on the wavelengths which engage in the greatest degree of diffraction and reflection. The tiny particles of debris in our atmosphere interact most with the smaller wave lengths of visible light (the blues), which is why the sky appears blue to us.
Of course we need to be extremely careful when even mentioning Genesis. That can rapidly drag the thread into an unintended direction. I'll say only that any story which has a planet form covered in water but without an atmosphere has things backward. Planets utilize their atmosphere to capture comets which contain a fair amount of ice and then to retain the water in that ice. If not for the barometric pressure exerted by the atmosphere, water would not remain liquid. It would quickly vaporize. And without the atmosphere to act as a retention bubble, the water vapor would simply drift into space. The same holds true of any claim that plants are growing on a planet which has no source of heat or light. Genesis suggests plants on day three, and the formation of the sun on day four. The plants mentioned are highly evolved species (grasses, herbs and fruit-trees). The first plants were far less highly evolved, likely resembling protists -- something closer to algae. Plants simply can't grow without light as they rely on photosynthesis to convert light into sugars upon which the plants feed. Take away the warmth of the sun and the Earth would be roughly the temperature of space, around 454 degrees BELOW zero, Fahrenheit (about 5° above absolute zero) -- not exactly an agricultural cornucopia.
Without attempting to step on any toes here, the evidence demonstrates that it's but a story written by people with a vast lack of understanding concerning some of the key principles of reality and bears no credible resemblance to any viable scientific theory. To engage this further would require a review of forum rules (I'm not sure it would be allowed), and a new thread.
