Wanting to Make Sprites, but Having Trouble Finding a Palette

[Virt]

I'm decent at spriting (some of you may have seen my Sonic Genesiserations Thread [also, I posted it in the wrong section, sorry]), but my main trouble is finding a palette. I'm wanting to sprite some things that take on a somewhat dark, dramatic feel, and I'm wondering what sort of palette I should use (I know darker colors, but I need exact colors). Help?