acid

coord = {x = 0, y = 0}
size = {x = 0, y = 0}
time = 0

function main()
  mon = peripheral.wrap("left")
  size.x, size.y = mon.getSize()
  local col = 0
  while true do
    sleep(0.05)
    time = time + 0.1
    for x = 1, size.x do
      for y = 1, size.y do
        coord.x = x
        coord.y = y
        col = pixel()
        mon.setCursorPos(x, y)
        mon.setBackgroundColor(getCol(col.r * 255, col.g * 255, col.b * 255))
        mon.write(' ')
      end
    end
  end
end

function pixel()
  local col = {}
  col.r = coord.x / size.x
  col.g = coord.y / size.y
  col.b = 0.5 + 0.5 * math.sin(time)
  return col
end

function sqr(x)
  return x*x
end

cols = {{240, 240, 240, colors.white},
{242, 178, 51, colors.orange},
{229, 127, 216, colors.magenta},
{153, 178, 242, colors.lightBlue},
{222, 222, 108, colors.yellow},
{127, 204, 25, colors.lime},
{242, 178, 204, colors.pink},
{76, 76, 76, colors.gray},
{153, 153, 153, colors.lightGray},
{76, 153, 178, colors.cyan},
{178, 102, 229, colors.purple},
{51, 102, 204, colors.blue},
{127, 102, 76, colors.brown},
{87, 166, 78, colors.green},
{204, 76, 76, colors.red},
{0, 0, 0, colors.black}}

function getCol(r, g, b)
  local dst = 0
  local best = 2147483647
  local col = 0
  for i = 1, #cols do
    dst = sqr(r - cols[i][1]) +
          sqr(g - cols[i][2]) +
          sqr(b - cols[i][3])
    if dst < best then
      best = dst
      col = cols[i][4]
    end
  end
  return col
end

main()