Is it possible to change the frequency of the light by magnetic fields? I do not recall where, but I have read someting about the light approaching a blackhole. In the writing, it was said that an object would gain kinetical energy due to the blackhole's gravity, and would increase its speed. On the other hand, when the light approaches than an object, it would gain kinetical energy as well, but the speed of it would not change: The frequency would. 
And so, an idea appeared in my head; since the mass-gravity is the weakest among gravities, what would happen if it was tried to affect the frequency of light through magnetism. Of course, even though the mass-gravity is the weakest, the blackhole is being talked of, so to be equal, a lot of magnetic force would be needed, doubtly. Yet, regardless of the ammount, I would like to learn if the statement I've read about is true, and if it is; I would like to learn if it is possible to affect the light by magnetism. 
 A: If I understand you correctly, you ask whether a magnetic field could change the frequency of light in free space just like a gravitational field can do. If you consider that gravitation is related by Einstein's field equations to the energy-momentum tensor which comprises not only matter, but also radiation and all not gravity related force fields, you can expect that also a magnetic field has a gravitational effect and thus should influence light at high enough field strength.
A: Classical electromagnetic fields, light one part of the frequency spectrum, are an emergent phenomenon from the superpositions of innumerable photons which have energy E=hnu, where nu is the frequency of the light beam and h is Planck's constant.
The statement that the frequency of light is affected by the gravitational field is true, because it is a gravitational interaction of the light beam, which carries energy,  as modeled by General Relativity. At the photon level the four vector describing the photons loses or gains energy according to the motion in the gravitational field.
The magnetic fields are a different story, photons may scatter off magnetic fields, at visible wavelengths with very small probability, so the frequency of the  light beam composed out of these photons is not affected when passing through a magnetic field. Photon photon interactionshave tiny probabilities at visible light energies, and exchanges of energy, which are necessary for a change in frequency, are very very low: the photons of the light beam would interact with virtual diagrams with the magnetic field, bringing the probability very low.
In conclusion , magnetic fields do not affect the frequency of light.
