Code:
alias test echo -a $hexrgb(255)
alias hexrgb {
  var %a = $base($gettok($rgb($1), 1, 44), 10, 16, 2)
  var %b = $base($gettok($rgb($1), 2, 44), 10, 16, 2)
  var %c = $base($gettok($rgb($1), 3, 44), 10, 16, 2)
  return $+(%a, %b %c)
}