Infra red filters are deep red. No surprise. However, people cannot see infra red, so a really good IR filter should appear opaque to the human eye. It is best to look at the spectral transmission curves of filters.
For example, I used an ultraviolet filter. It had a filter factor of about 10 stops, and I could not see through it. The b&w results were totally unpredictable and unusual.
True UV and IR photographs have some interesting forensic uses. I took some images of the Santa Barbara Mission. I could easily see where the building had been rebuilt after major earthquake damage (and repainted). The building looked normal to the eye, but the new construction was easy to see with true UV and IR.
Don't forget that the autofocus on cameras may not work with IR.