Dynamically create classes with SASS (from http://www.paulund.co.uk/dynamically-create-css-classes-sass)

_process.scss

$colours:
	"red" #FF0000,
	"blue" #001EFF,
	"green" #00FF00,
	"yellow" #F6FF00;

@each $i in $colours{
	.#{nth($i, 1)}-background {
		background: nth($i, 2);
	}
	.#{nth($i, 1)}-color {
		color:nth($i, 2);
	}
}

output.css

.red-background {
	background: #FF0000;
}

.red-color {
	color: #FF0000;
}

.blue-background {
	background: #001EFF;
}

.blue-color {
	color: #001EFF;
}

.green-background {
	background: #00FF00;
}

.green-color {
	color: #00FF00;
}

.yellow-background {
	background: #F6FF00;
}

.yellow-color {
	color: #F6FF00;
}

You no longer need to 'nth' when you use the @each

$colours:
"red" #FF0000,
"blue" #001EFF,
"green" #00FF00,
"yellow" #F6FF00;

@each $key, $value in $colours{
.#{$key}-background {
background: $value;
}
.#{$key}-color {
color: $value;
}
}