You can't make the reader see a precise shade of color, as a visual artist can. Not only for blue, but for robin's egg blue or sapphire, or navy. Even if a color term has just one shade, the reader can misremember it.
So instead as a prudent writer, you take advantage of the way you can do what the visual artist can't: load your language. Can't do it too heavily, or it will betray its presence too much, but it works.
One consequence is that you can use colors to associate heroes and villains where the visual effect would be less particular. Though some of the associations need more development. Especially for Evil Overlords where the association generally works best if played up to make the character seem more like a force of malevolence than a human.
White is lily or star for good; snow can indicate purity or deathly cold; bone and salt goes easily into evil.
Black is generally darkness and therefore ignorance and danger, but it can be spun as a sober color or even as taking in all light as a beneficent trait.
Gray is a sober color, too. Mists are not bad but need some loading. Ash, on other hand --
Brown is earthy and the wild. Can go either way, with some emphasis on savage beasts for the evil.
Purple is royal/imperial which could go either way, if loaded toward "tyrant" or "good king." Also associated with mourning, which also needs to be handled to determine how it will spin.
Red is roses and sunrises and other cheerful associations; also blood and fire, easily pointed toward evil.
Orange is fire, which is fairly easy pointed toward evil, but it's also associated there with hearth and therefore home. Needs careful loading.
Yellow is good as wheat, evil as jaundice -- sunlight is usually good, but if you associate it with deserts, can shift. Gold needs to be loaded, as it is brilliant and precious and durable, but can be used to indicate greed. (And jewels, regardless of color, can be used the same way.)
Green is leaf green and life and goodness -- or poison or snakes or of course both at once.
Blue is heavenly and so good. I was having trouble thinking of bad blues -- except where it's cold, and usually people use white for that -- but then was thinking about the blues, and how water is often falsely depicted as blue. Sorrow and tears. Which would produce a very different Evil Overlord than the classic red and black.