Polyfill gray() from CSS Color Level 4 with Stylus

gray.styl

/*  Based on "Polyfill gray() from CSS Color Level 4 with SASS"
 *  by Lea Verou
 *  with revisions by Chris Eppstein
 *  https://gist.github.com/LeaVerou/9199277
 */
 
gray(intensity, alpha = 1)
  rgba(intensity, intensity, intensity, alpha)

/* Testing our new function */
body {
	background: gray(50%);
	background: gray(255, .2);
}
 
/* Test should output something like: */
body {
  background: #7f7f7f;
  background: rgba(255, 255, 255, 0.2); }