Modern Color-Light Signal
Based on these ubiquitous signals that are rapidly replacing classic signals along most North American Railroads. Most often called "Darth Vader signals" because the large sun-hood looks quite like Vader's helmet.
The signals appear lit thanks to white 1x1 rounds behind the "lit" colors and black behind the other colors.
Using this technique for signals lights is a versatile means to produce reasonably realistic "lit" signals without going to the trouble of wiring them (although that is my long-term goal).