I found these at SimplaVortaro.org:

Saffron = Safrano => Safrana
Fuchsia = Fuksio => Fuksia
Celadon = Celadono => Celadona
Vermillion = Vermiljono => Vermiljona
Cinnabar = Cinabro => Cinabra
Lavender = Lavendo => Lavenda

These seem to be more-or-less straightforward renderings of the names into Esperanto orthography. The rest don't show up at SimplaVortaro, but why not apply the same method to them? I suggest:

Viridian = Viridjano => Viridjana
Cerulean = Ceruljano => Ceruljana

The only difficulty is Pewter. Rather Anglo-Saxon, not Latinate/Romance like the rest. If you render it as "Peuxtra" it sounds too much like "Putra", which conveys quite the wrong idea. Google Translator seems to translate it as "Tin" in every other language. That makes about as much sense as translating "Bronze" as "Copper". But how about this:

Pewter = Tin-Alloy = Stanalojo => Stanaloja

Pewter is tin alloy containing a very high percentage of tin. How different the colour of pewter is to the colour of the pure metal I don't know.

'Stangriza' might not be technically accurate - depends on the colour of the metal as opposed to the alloys.

Pewter as a colour term is clearly a sort of grey, I would think of it as being quite close to the colour of lead but not quite so dark.

Perhaps 'metal-griza' or 'hel-plumba' or 'ŝtal-griza' covers it.

'Stanaloja' however clearly sidesteps the issue of what precise colour pewter is - so that could be a neat solution.

Well, that was the point I was trying to make. These are mostly names for exotic objects and substances, not colors per se, although they imply the associated colors obliquely. It completely misses the mark if you simply translate them into pedestrian names for approximately-similar colors, you lose all the exotic poetry of the originals. Best to focus on translating them into Esperanto names for the same exotica (or as close as you can get) and preserve the same oblique slant on the colors.

That's why Stanaloja would be a better bet than Stangriza. With Stangriza, you're beating the gamers over the head with the fact that it means "grey". With Stanaloja, they figure it out for themselves. Much cooler that way.

I'm curious how Vespero is going to tackle the really big job: coming up with Esperanto names for all the species of Pokemon! Every one of them is a pun of some kind. How do you render those into a language designed to avoid puns?

You make a good point too. The reason I chose ordinary-sounding translations was because half of those words I didn't know myself in English, and they just sound exotic to me. ('Vermillion' I really did learn from Sesame Street!) Better to use something simpler, I figure, and let the fact of it being a foreign language take care of making it sound exotic.

Kodegadulo:How do you render those into a language designed to avoid puns?

Well, it doesn't avoid puns, just has different types (refer to this thread)