Like a spotlight: from the side it shines dim red, but head-on it's dazzling white-blue. That's exactly how the mysterious 'little red dots' in the early universe appear: they are giant black holes turned edge-on toward us. The thick disk of scorching gas surrounding them hides the brightest radiation, letting only a soft reddish light and the glow of hydrogen through, as red as a neon sign.
Before, astronomers debated: maybe these are dense clumps of stars or the ultra-bright centers of galaxies. But the spectral fingerprint of their light, stretched by the expansion of space, revealed a familiar signature — the same as a stellar pair in the Milky Way where a black hole devours its neighbor.
The prototype of the red dots, the SS 433 system in our Galaxy, shoots out plasma jets at a quarter of the speed of light, blowing a bubble hundreds of light-years across.
In Star Wars, the color of a lightsaber signals your side of the Force; in space, the color of a distant black hole depends on the angle: red when seen edge-on, and blue when staring you straight in the face.