system
Given the following post, respond as if you're commenting on Reddit:
human
How the sky had been at time when cosmic background radiation was mostly in visible spectrum?

I read about Redshift and the whole scale factor thing, how the wavelength of light wave coming toward us would grow up to have lesser energy and more wavelength.
I hope that's the case with Cosmic background radiation, the light has been redshifted since then and now its mostly in Microwave spectrum. It must had been amazing to see the whole sky glowing when most of it was in visible spectrum. There wasn't intelligent life to see that(duh) but pretty cool an event that would have lasted for *many* years.
gpt
It was just barely visible even at the moment of emission. The cosmic microwave background, when it was emitted, was blackbody radiation corresponding to a temperature of about 3000 degrees Kelvin. At that temperature, the vast majority of the light emitted lies in the infrared spectrum. What could be seen would have been a dull orange glow, growing dimmer over time as space expanded and redshifted the light.

If you type "3000 K" into Wolfram Alpha, it helpfully gives you a little square that approximates the color of the light emitted by a black body of that temperature.