Krita has its own reference picture tool, but you can also use the great plugins from @EyeOdin and @freyalupen, Imagine Board and Reference Tabs Docker, but, reading your request, I would tend to Imagine Board.
And if you are looking for the Swiss Army Knife of colors, you should check out the marvelous plugin Pigment.O, also made by @EyeOdin.
Michelist