The photons are real yes.
But our receptors are tuned to certain frequencies only.
there are far more colors than we can ever see.
are we looking at colors or hearing sounds or feeling vibrations with our bodies ? it depends on our species and our senses
I agree that they are real.
But I also understand why other people say it’s an illusion.
it’s not an illusion because that’s just how we work in our relationship with the world.