SASS looping over colors creating nth-child selectors

input.sass

li
    $colors: rgb(230,196,19), rgb(233,171,48), rgb(222,65,56), rgb(158,48,49), rgb(64,13,45), rgb(120,40,109), rgb(188,33,135)
    $num: 0
    @each $color in $colors
        $num: $num + 1
        &:nth-child(#{$num})
            background-color: $color

output.css

li:nth-child(1) {
    background-color: #e6c413;
}
li:nth-child(2) {
    background-color: #e9ab30;
}
li:nth-child(3) {
    background-color: #de4138;
}
li:nth-child(4) {
    background-color: #9e3031;
}
li:nth-child(5) {
    background-color: #400d2d;
}
li:nth-child(6) {
    background-color: #78286d;
}
li:nth-child(7) {
    background-color: #bc2187;
}