Spectra

The game is played on a 4x4 square board with 16 transparents discs, 5 each of red, yellow and blue and one colourless disc.
Players take turns in placing two single discs onto the board in vacant spaces until the board is full. Players now may move two single discs each turn but now they may be placed one piece on top of an existing piece but never such that there is more than two in a stack. A red piece on a blue (or vice versa) produces the colour purple and similarly yellow plus blue produces green and yellow plus red produces orange.
The winner is the first person to produce an orthononal line of four or a square of four of the same colour (red, yellow blue, green, purple or orange).