Is the speed of light constant between galaxies?

Dark matter found between galaxies Dark Matter Filament Between Galaxy Clusters Found | Space using gravitional lensing.Would light (photons) slow down going through these energies or would light bend around "dark matter" and follow its contours and nothing is where we believe (outside of our galaxy)?.HALL OF MIRRORS - SCATTERED PICTURES.If 80-90% of universe is "dark matter" and light does not interact but bends around "dark matter" there would be alot of bending, so are the galaxies where we really think they are?Which in turn would mean if we could ever fly through "dark matter" as the crow flys, could we reach a destination before light, that travels a long and winding path around the dark matter, which would be a long detour if dark matter makes up 80-90% of universe.Or does light slow down while passing through dark matter like it does through glass, retaininng its light speed once it as passed through?Would this also mean that neutrinos cannot travel faster than light but they can travel straighter than light, and pass through dark matter?Is there any real proof, light speed is constant between galaxies?

There is much guess work about the properties of "dark matter", from what i can deduce light does not interact with dark matter, We can only summise where it is by the effects of gravitational lensing, if this is correct, with the amount of estimated dark matter in our "local universe", i see the possibility of it being like a "Maze" where light enters at one destination and exits at another or multiple others, so we are almost never looking directly at distant galaxies,
Perhaps something like how a periscope works.Sometimes we need to think aloud, and see if we are missing something obvious, i have my picture of how it all fits together, but if i am wrong on parts of that picture it will not be a complete picture, so i would welcome any views on how dark matter effects "light".Or if you wished i could add this to my last post
EvC Forum: Alpha-Omega universes in free fall Alpha-Omega universes in freefall.But i would prefere a new thread, as there are a few ideas i have about "dark matter" that i would like to ask those with a better idea than myself on sub atomic particles.Edited by sunshaker, : added link to old post.Edited by sunshaker, : No reason given.