A function to adjust the lightness of a color in Javascript. Based on a solution from http://stackoverflow.com/questions/5560248/programmatically-lighten-or-darken-a-hex-color

adjustLightness.coffee

adjustLightness = (color,percent) -> 
  num = parseInt(color.slice(1),16)
  amt = Math.round(2.55 * percent)
  R = (num >> 16)           + amt
  B = (num >> 8 & 0x00FF)   + amt
  G = (num      & 0x0000FF) + amt
  "#" + (0x1000000 + 
    (if R<255 then (if R<1 then 0 else R) else 255)*0x10000 +
    (if B<255 then (if B<1 then 0 else B) else 255)*0x100   +
    (if G<255 then (if G<1 then 0 else G) else 255)
  ).toString(16).slice(1)