I don't think all of the lamps were red. My recollection is that in the past they were black but some were red, maybe in more recent times.
The lenses on the LC were red I think as the burner would be clear but I suspect the lenses on a signal lamp were clear as they semaphore red & green lenses need to show the correct color aspect. There was a thread on the site before with some additional detail. I'll post a link IF I can find it.
Recent, Buttevant LC, 2012
Again, Black LC lamp with red (definitely not clear versus red on gate) lens
This looks like your cutout on the back of your lamp. Possibly to aid lighting while on the ladder?
Some signal lamps definitely had a lens on the opposite white side of the semaphore. I ind; know if the lens was white or red (probably) but it was visible with the signal at danger and occluded by a backing plate on the semaphore when clear