I THINK a blue star would make him even more powerful and an orange one would make him still superpowered, but weaker as it's closer to red.
So you think his power is related to the wavelength of light and not by the energies outputted by the star, its type or other factors I would think could be more at play than the wavelength of the light.
Uhh, what? Those are all the same thing. The peak wavelength of light given off by a star is inversely proportional to its energy output (i.e. the peak frequency is directly proportional to its energy), and a star's spectral type is defined
by its peak wavelength. A blue star is hotter than a yellow star is hotter than a red star. The reason (post-Crisis) why Superman gets superpowers from a yellow star and not a red star is because a yellow star is more energetic and thus "supercharges" his cellular batteries.
The comics and other fiction have been inconsistent about the effects of blue stars. Elliot S! Maggin's Superman novels said that blue starlight would give Superman diminished powers, somewhere between his yellow-star and red-star conditions, but I don't think the reason for this was explained. In some recent comics, it's been asserted that blue stars give Superman, not greater powers, but additional
powers, specifically the ability to induce Kryptonian superpowers in others via a beam from his eyes. Don't ask me, I'm just the messenger.
Are their viloet or ultraviloet "stars"? How would a blackhole effect him?
O-type stars do peak in the ultraviolet. But we're talking about a blackbody spectrum here, and the color of a star is its peak wavelength, not its only one. A hotter star would have its peak further toward the blue/violet end of the spectrum, but would still be even brighter in the red, orange, yellow, green, etc. bands. So while an O star's peak is in the UV, the starlight still appears blue to the observer.
As for black holes, they're just plain black -- no energy output at all, by definition. As long as Superman's far enough away to be unaffected by its gravity (and despite sci-fi mythology, a black hole's gravity is no more "sucky" than that of a star of equivalent mass, and is only dangerous if you get really close), he'd get no energy from it at all and it would be no different from being exposed to empty space. Unless it has an accretion disk of infalling matter, in which case the inner portion of the disk would be so hot as to be giving off x-rays and gamma rays. However, in order for a black hole to have an accretion disk, it would pretty much have to be orbiting a star (another thing that mass-media depictions of black holes almost invariably get wrong), so Superman would be affected by that star's light in the usual way.