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HTML 

              
                %h1 Rainbow with Sass & Compass

%h2 My Rainbow:

.my-rainbow

%p
  For a website, I wanted to make a reusable mixin
  that uses CSS background gradients to create a
  colour stripe effect. My version was hard-coded to
  take 8 colour values. It also was pretty verbose.
  Finally, it only allowed stripes to go from left
  to right.

%p
  I knew it could be done much better, so I
  %a(href="https://twitter.com/jina/status/225811628338323458") tweeted out a request
  for a Sass expert to show me a better way to write
  my mixin.
%p
  Shortly after I tweeted that, I received an
  %a(href="https://twitter.com/eriiicam/status/225830655622254592") amazing contribution
  from @eriiicam. I was amazed at what Sass is
  capable of doing. They look identical, but with his
  improvements, I can give it as many colours as I
  want, and I can have the stripes go in whichever
  direction I want. It's also not verbose like mine was.

%h2 His Rainbow:

.his-rainbow

%p
  A huge thanks goes to Eric for his help on this.
  I thought it was so cool that I wanted to share it
  here. While I posted the idea for the mixin, I want 
  to stress that Eric did the Sass Function. I hope 
  you find it as helpful as I did.:)
!

CSS 

              
                @import compass

$link: #369

body
  padding: 24px
  font: 16px/1.5 Helvetica, Arial, sans-serif
  background: #fff
  color: #444

a
  text-decoration: none
  &:link,
  &:visited
    color: $link
  &:hover,
  &:focus
    color: darken($link, 10%)
  &:active
    color: darken($link, 20%)

h1,
h2
  margin: 0
  padding: 1em 0 0
  font-size: 1em
  text-transform: uppercase
  color: #888

h2
  color: #666

// -------------------------------------------
// MY VERSION

$stripe-width:  100% / 8

$stripe-1: #c00
$stripe-2: #f90
$stripe-3: #ff6
$stripe-4: #693
$stripe-5: #3cc
$stripe-6: #09c
$stripe-7: #33c
$stripe-8: #96c

=rainbow
  +background-image(linear-gradient(left, $stripe-1, $stripe-1 $stripe-width, $stripe-2 $stripe-width, $stripe-2 $stripe-width * 2, $stripe-3 $stripe-width * 2, $stripe-3 $stripe-width * 3, $stripe-4 $stripe-width * 3, $stripe-4 $stripe-width * 4, $stripe-5 $stripe-width * 4, $stripe-5 $stripe-width * 5, $stripe-6 $stripe-width * 5, $stripe-6 $stripe-width * 6, $stripe-7 $stripe-width * 6, $stripe-7 $stripe-width * 7, $stripe-8 $stripe-width * 7, $stripe-8))

.my-rainbow
  height: 1em
  +rainbow
  +box-shadow(0 1px 2px rgba(#000, .25) inset)



// -------------------------------------------
// HIS VERSION

// Using the above colours
$colours: $stripe-1, $stripe-2, $stripe-3, $stripe-4, $stripe-5, $stripe-6, $stripe-7, $stripe-8

@function stripes($position, $colours)
  $colours: if(type-of($colours) != 'list', compact($colours), $colours)
  $gradient: compact()
  $width: 100% / length($colours)

  @for $i from 1 through length($colours)
    $pop: nth($colours,$i)
    $new: $pop ($width * ($i - 1)), $pop ($width * $i)
    $gradient: join($gradient, $new, comma)

  @return linear-gradient($position, $gradient)

.his-rainbow
  height: 1em
  +background-image(stripes(left, ($colours)))
  +box-shadow(0 1px 2px rgba(#000, .25) inset)
!

JS
!
999px

Console