Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.0.rc.3)
// Compass (v1.0.0.rc.1)
// ----

//Thanks:http://sachagreif.com/useful-sass-mixins/
@function black($opacity){
  @return rgba(0,0,0,$opacity)
}
@function white($opacity){
  @return rgba(255,255,255,$opacity)
}
//Usage:
.my-class{
  background:black(0.15);
  color:white(0.9);
}

SassMeister-output.css

.my-class {
  background: rgba(0, 0, 0, 0.15);
  color: rgba(255, 255, 255, 0.9);
}