Is there not also a metal that is faintly bluish/lilac in colour? (the metal itself, without oxidation) I seem to remember that there was one, but can’t recall what it was.
I think a few metals have a hint of blue, but they’re still mostly gray. I did find that tantalum and cadmium can appear a bit bluish.
Cobalt, oddly, does not look blue at all to me in pure form, even though it’s famous for being used to make blue dye.
Yeah, it’s quite yellowish.
I still don’t know WHY most metals are grey and only three aren’t.
Interestingly, copper and gold are in the same group, group 11, but cesium is not. Cesium is in group 1 with other scarily reactive metals.
It was alluded to in the first response. In metals, their outer (valence) electrons are shared in an electron “sea”. This is why metals are comparatively good conductors, and some are excellent conductors.
This electron sea has density oscillations with a characteristic frequency, and these oscillations interact with the field of EM radiation to either transmit or reflect depending on frequency of the EM radiation.
Some details here.
When we do the math / chemistry / quantuming, we find that for almost all metals the characteristic frequency is greater than visible light, so, to our eyes, they reflect all frequencies completely. When their surfaces are very smooth they may function very well as a mirror.
If we had an evolutionary reason to differentiate elemental metals, we might have evolved (again) a UV-sensitive color cone in our eyes. Then they would appear different shades.
Cobalt blue is a mixture of cobalt oxide and aluminum oxide. So the color of the pure metal is irrelevant.
Similarly, the pigments with chrome in their names are compounds and not metalic chromium.
OTOH, Prussian blue is made out of real live Prussians. 
I think you mean real formerly live Prussians. 
Depends how quickly you use their parts.
They’re live when the pigment is made.
Osmium metal is faintly blue.
I think its tetroxide is also strongly colored, but I’m talking about the bare metal itself.
As an aside, aluminum does oxidize fast, forming a stable solid and very hard oxide, alumina – also known as sapphire if it’s a single crystal.
This creates a special vulnerability. If you get gallium metal, even a droplet, onto a piece of aluminum, the aluminum is doomed. Gallium is very much like aluminum, except that its melting temperature is around room temperature. The aluminum dissolves into the gallium. Like all liquid solution, the aluminum diffuses around in the gallium. But atoms that happen to make it to the surface oxidize very quickly. Trouble is, this nice hard oxide is now on a liquid, and can’t form a protective coating, so the oxidization keeps going. A drop of gallium can destroy a big chunk of aluminum, and short of cutting the contaminated aluminum away, or putting the whole deal in an anaerobic environment, there’s no stopping the process. For this reason, IIRC, gallium is not allowed on aircraft.
They make a commotion that really distracts you from your work, though.
Video of this rather arresting phenomenon. The fun starts at 3:00.
Or ruby.
Or pulling apart aluminium padlocks after using a gallium “key”
Reminds me of firehouse slang. They have what they call a “universal master key.” It can open any door. It’s actually a 250lb musclehead firefighter with a big axe.
And gasoline powered chain saws & circular saws in back-up for the really hard cases.
I was interested to Google [Buy gallium] and see it was easy to get and not very expensive. Remind me not to buy any aluminum padlocks.
I wouldn’t be too concerned. A thief has to know it’s aluminum and/or bring gallium just in case. It’s not very likely in practice.
They are much more likely to bring bolt cutters or just chance upon a bike or whatever that the owner forgot to lock.
Of course, if it’s a bike, they’d have to be careful not to get it on the bike or they destroy what they tried to steal.
$29 for about half an ounce on Amazon. Which isn’t much, but it’s enough for a cool experiment.
Mercury does the same thing.
But mercury isn’t a solid at room temperature* and is much more toxic. I wouldn’t recommend it for amature experiments.
*granted, Gallium isn’t solid in a warm room, but that’s half the fun anyway.
Compared to other silvery metals, zinc is…blue-ish.