Very cool snippet BlueThen. I definately see how this could be usefull but when I tested it I seemed to have problems. I went to shorten your code a little bit and my output was different than yours and I finally realized why. I thought I was messing mine up and infact I had discovered a mistake in yours. You have a $2 in the $3 line.

Heres my ideas to shorten it a little bit. I just used a while loop to make the 1 if line handle all three $'s. I also added a check for $3 to make sure that it exists and I didnt totally understand your calc's when I thought there was an error so I made a new one which seemed to test just fine and is shorter than the one you came up with.

alias brgb {
  if ($3) {
    var %brgb.r, %brgb.g, %brgb.b, %endnum $0 
    while (%endnum) {
      var %dotletter $iif(%endnum == 3,b,$iif($v1 == 2,g,$iif($v1 == 1,r))), %dollarnum $ $+ %endnum 
      if ($(%dollarnum,2) > 255) %brgb. [ $+ [ %dotletter ] ] = $calc(255 - ($(%dollarnum,2) - (255 * $int($calc($(%dollarnum,2) / 255)))))  
      else %brgb. [ $+ [ %dotletter ] ] = $(%dollarnum,2)
      dec %endnum
    }
    return $rgb(%brgb.r,%brgb.g,%brgb.b)
  }
}

Anyhow, mine isn't a whole lot shorter but I think it is definately shorter and does show a bit of a different way of doing things for anyone looking.

I really do like the idea and like I said it does make sense and people should find it usefull.

Well done.