BizHawk Color creation function

function gui.color(r, g, b, a)
  if not a then
    a = 255
  end

  r = math.floor(r)
  g = math.floor(g)
  b = math.floor(b)
  a = math.floor(a)

  if a > 127 then
    return (r * 65536 + g * 256 + b) - ((256 - a) * 16777216)
  else
    return a * 16777216 + r * 65536 + g * 256 + b
  end
end