In everyday context yes, but it’s pretty common to use “colour” to refer to frequency outside the visible range, and it’s interesting to consider what interesting “colours” we are missing out on because they’re outside our visible range.

Silver/grey implies even response across the spectrum, and is the normal expectation.

If we couldn’t see yellow (red/green) then gold would presumably look silver to us, so are there silver/grey metals that would have an interesting colour if only we could see it?

Well infrared goes the other direction. Along with radio.

If a bee sees a color we cannot, it would be pretty silly to insist it's not a color on the basis of us being unable to see it, wouldn't it?

... when charged particles move faster than the speed of light

So that got me curious, and found this

nothing travels faster than light in vacuum, but light can be slowed down and something can travel faster than this "slower" light

Somehow I've gone through decades of life without knowing this..

uranium itself isn't, anything will glow that colour if it undergoes nuclear fission underwater.