@each loop with index

First of all, the @each function is not from Compass, but from Sass.

To answer your question, this cannot be done with an each loop, but it is easy to convert this into a @for loop, which can do this:

@for $i from 1 through length($refcolors) {
    $c: nth($refcolors, $i);

    // ... do something fancy with $c
}