Father, Today I visited a church in a nearby town in a different diocese. The Bishop in that diocese sent out a letter about a year ago that all tabernacles are to be in front of the church. This parish had the tabernacle in the back in a room all it’self and they left it there, but put another one in front. They both have a white lamp! I was with a friend from that town & he was not surprised. I wondered if that lamp is allowed to be in a white or clear glass instead of a red one.
The color of the sanctuary lamp is often red, but this isn’t prescribed anywhere. The burning lamp in many places indicates that the Eucharist is reserved there. I would say that the use of a red lamp is so common that using a different color is not a great idea. It caused confusion for you to see a white one.
In Roman churches there can be also as many as 7 lamps hanging before the tabernacle.
Another way to show that the Eucharist is present, is to have a veil on the tabernacle and/or baldachin.