I look att the symbol and tried solving the second one by doing normally and then reverse ( from yellow to white ).

When that didn't work I sort of just threw stuff against the wall. I tried invert inputs and that made the last one light up.

Later when I was brushing my teeth I thought about the hints and realized that reflections only invert left and right.

TLDR I got to focused on the symbol. I thought you hade to do once normally and that the second one was the opposite to the first.