You know how white light, is a conglomeration of existing color frequencies?: Do other EM bands hold "riff raff"; 'pseudo-white', type thing?

White light is actually the perception our eyes (and brain) get from being exposed to the full "blackbody" radiation spectrum of a source at 6000 K (roughly 10,340 F).

Because we have evolved in daylight of that "colour temperature", the brain interprets the mixture received by the color receptors in the eyes, as "white", the perfect color. It represents the natural light we get from the Sun (roughly 5500 K) and the blue of the sky (close to 10,000 K).

Stars with a surface cooler than that of our Sun will have a spectrum that has less high-energy photons (i.e., blue light); they will therefore appear yellow (for ex., Arcturus) or even red (Antares).

Monochromatic (single color) light sources do exist. Lasers are often monochromatic (a laser will emit one single frequency for ALL its photons).

https://en.wikipedia.org/wiki/Laser#/media/File:La...

Some gasses, when excited - for example, by running high-voltage electricity through them - will also emit light that has very specific colours.

For example, neon gas glows red.

Since such a device is more efficient that the old tungsten (filament) light, you would get much more light for the same amount of power. Many lights containing low-pressure gasses are often called "neon light" even though the gas inside contains no neon at all.

https://en.wikipedia.org/wiki/Neon_lighting

For a while, yellow street lights were popular. The low-pressure kind emit a monochromatic yellow light, while the high pressure type emits many different colors which adds up to "yellow" for our brain.

https://en.wikipedia.org/wiki/Sodium-vapor_lamp#/m...

It is possible to create white light (or, at least, something our brain will interpret as being white) by adding together light sources of dominant primary colors (the easiest trick is to use red, green and blue - other combinations are possible).

https://en.wikipedia.org/wiki/RGB_color_model#/med...

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Visible light is just a tiny part of the entire electromagnetic (EM) spectrum. When you create a simple antenna (for example, a length of wire), it will be sensitive to a large band of frequencies. Unless you have a tuner, a detector will simply capture the energy. The higher the energy, the "brighter" the radio spectrum it receives. If you have a signal that shows up on many or all channels (once you have installed a tuner), then that signal covers a wide spectrum (it contains all the radio "colors").

We (humans), wanting to use radio to transmit in an efficient manner, would use very narrow band of frequencies in order to conentrate the energy, thus sending music and commercials over longer distances.

In older black-and-white TV sets (the ones with rabbit ears on top), the channels 2 to 6 would be filled with static (when they were not in use in a particular area). That was the effect of the Cosmic Microwave Background radiation emitted everywhere in space, roughly 13.8 billion years ago.

When you analyse the entire spectrum of this CMB radiation, you find that it is equivalent to the black-body radiation of a source just below 3 K.

If you could have a simple antenna tuned to that spectrum, it would appear "white".

If that is what you mean, by "pseudo-white", then yes, it exists.