Tri-colored VASI
This is a single light that appears amber above the glide slope, green on the glide slope and red below it. It is rarely used, partly because pilots who are unfamiliar with them have been known to misinterpret the lights, causing them to 'correct' in the wrong direction. Despite this shortcoming, it is (reportedly) in widespread use in Eastern European countries, especially Russia and Ukraine.
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I've flown a tri color vasi once...what can I say...it works as advertised.