they might be more grey than blue.
Brown, huh? What do you think about using a slate or pewter color...like dark grey colors?

If you want them to look more blue, or to stand out I think chocolate brown is the best. Don't go too dark, you should be able to see that it is brown and not black.

Brown makes them stand out more.

Well, let's see. If you have quite pale skin, go with a brownish mocha type color, if you have tan skin, I would go with sort of a dark brown, and if you have quite dark skin, I would go with a black color. It really depends on the kind of look you want, if you want a colorful sort of mod look, and you have light skin, I personally think that white eyeliner looks amazing. And since you have blueish grey eyes, you would want to do maybe some purpley colors for eyeshadow, or greens, but don't use blues, because they will distract from your eyes. If you want a very natural, classic look, than go with a brown, or for dark skin, black. For a smokey eye, which looks beautiful with blue eyes, and really accents them, do a thin, black eyeliner, with greys and charcoals for shadow. But since you say that your eyes are a bit greyish, I think the smokey eye might detract from your eyes. Hope this helps!