Sass color variable not working inside darken()

I've got list of colors and I would like to use darken() on them like so:

$innerPagesBgColors: "#6B46C1", "#2980B9", "#FD5456", "#000";

.foo {
    color: darken(nth($innerPagesBgColors, 3), 5%);
}

But I get this error:

$color: "#FD5456" is not a color for `darken'

I tried interpolating the nth() portion but that didn't help either.