Gui, Add, Picture, x100 y100 w2 h2 +0x4E +HWNDhPicture
CreatePixel("FF0000", hPicture)
Gui, Show, w320 h240, Example
return

CreatePixel(Color, Handle) {
    VarSetCapacity(BMBITS, 4, 0), Numput("0x" . Color, &BMBITS, 0, "UInt")
    hBM := DllCall("Gdi32.dll\CreateBitmap", "Int", 1, "Int", 1, "UInt", 1, "UInt", 24, "Ptr", 0, "Ptr")
    hBM := DllCall("User32.dll\CopyImage", "Ptr", hBM, "UInt", 0, "Int", 0, "Int", 0, "UInt", 0x2008, "Ptr")
    DllCall("Gdi32.dll\SetBitmapBits", "Ptr", hBM, "UInt", 3, "Ptr", &BMBITS)
    DllCall("User32.dll\SendMessage", "Ptr", Handle, "UInt", 0x172, "Ptr", 0, "Ptr", hBM)
}