Yes, UV light encompasses a spectra range between 100-400nm. However, only the ~250-100nm range is able to penetrate the Ozone layer, so for all intents and purposes, natural sunlight UV on Earth can be considered to consist of ~250-100nm.

Yes, that is the definition of "color" in general. We are not able to SEE all colors that reflect, even though we are able to 'notice' enhanced UV brightening. But yes, all things in Heaven and Earth reflect light of certain wavelengths, which gives them their physical property of color.

Two parts to this answer:

As the sun rises or sets, the light 'rays' are penetrating the atmosphere at shallow angles. The first to 'fade', which is to say the first to start getting absorbed and/or reflected away from the surface by the Ozone Layer is the UV band. Longer wavelength light waves are better able to penetrate to the surface, which is why you'll see oranges and reds in the atmosphere as the sun rises and sets (the opposite end of the spectrum), rather than appearing BLUE as it does for the rest of the day - the blue, which is near the UV end, starts to get rejected/absorbed, and the reds/oranges/yellows start to dominate the penetrating light composition.

Beyond that, you have to consider how animals view "color" and light. The human eyeball contains two types (and a few subtypes within those two) of photoreceptors, rods and cones. When light intensity is high, the Cones are active, which allows us as humans to perceive colors. As a given wavelength of light enters the eye, it triggers different combinations of Red, Green, and Blue responsive cones, and the brain compiles those signals into their particular respective color. In low light conditions, the cones switch off, and the higher population Rods take over. Rods are NOT color sensitive, and only perceive intensity of total light in shades of grey.

So as the sun goes down, UV light gets scrubbed out, and the low intensity light triggers the eye to SWITCH OFF the color sensitive receptors in the eye. So bluntly - you can't see in color when it's dark, and "purple light" wouldn't be there to be seen if you could.

Couldn't agree more.

And again, the science doesn't support what hunters have misconstrued to be facts about UV perception of game animals and how important it is in terms of what you wear afield. When the light is high, the visible spectrum of light dominates the light field, and as light fades at dusk or dawn, the UV presence is even lower than it was at mid-day.

woof... Gotta take my nerd cap off now...