<===> input.scss
$params1: #fff .5;
test {
  color: rgba($params1...);
}

$params2: 10 250 130 .5;
test {
  color: rgba($params2...);
}
<===> output.css
test {
  color: rgba(255, 255, 255, 0.5);
}

test {
  color: rgba(10, 250, 130, 0.5);
}