TSMkr

os.loadAPI("TabletAPI")
local gpu = peripheral.wrap("right")
local _x, _y = gpu.getSize()
local r = 0
local b = 0
local g = 0
local s = 1

TabletAPI.clear(gpu)



local function drawBar()
  gpu.setColor(141, 141, 141)
  gpu.filledRectangle(0, _y-30, _x, _y)
  gpu.setColor(81, 81, 81)
  gpu.filledRectangle(0, _y-30, _x, 1)
  gpu.setColor(0, 0, 0)
  gpu.drawText("R: "..r, 1, _y-27)
  gpu.drawText("G: "..g, 1, _y-18)
  gpu.drawText("B: "..b, 1, _y-9)
  if s == 1 then
    gpu.setColor(255, 0, 0)
    gpu.drawText("R: "..r, 1, _y-27)
  elseif s == 2 then
    gpu.setColor(0, 155, 0)
    gpu.drawText("G: "..g, 1, _y-18)
  elseif s == 3 then
    gpu.setColor(0, 0, 255)
    gpu.drawText("B: "..b, 1, _y-9)
  end
  gpu.setColor(81, 81, 81)
  gpu.filledRectangle(35, _y-30, 1, 30)
  gpu.setColor(r, g, b)
  gpu.filledRectangle(40, _y-25, 20, 20)
end

while true do
  drawBar()
  ev, key, x, y = os.pullEvent()
  if ev == "key" then
  if key == keys.up then
    if s == 1 then
      s = 3
    else
      s = s - 1
    end
  elseif key == keys.down then
    if s == 3 then
      s = 1
    else
      s = s + 1
    end
  elseif key == keys.left then
    if s == 1 then
      if r == 0 then
        r = 255
      else
        r = r - 1
      end
    elseif s == 2 then
      if g == 0 then
        g = 255
      else
        g = g - 1
      end
    elseif s == 3 then
      if b == 0 then
        b = 255
      else
        b = b - 1
      end
    end
  elseif key == keys.right then
    if s == 1 then
      if r == 255 then
        r = 0
      else
        r = r + 1
      end
    elseif s == 2 then
      if g == 255 then
        g = 0
      else
        g = g + 1
      end
    elseif s == 3 then
      if b == 255 then
        b = 0
      else
        b = b + 1
      end
    end
  end
  elseif ev == "monitor_down" or ev == "monitor_move" then
    TabletAPI.setPixel(gpu, math.ceil(x/4), math.ceil(y/4), {r, g, b}, 4)
  end
end