But how do I get them?
Two of them you can find on the cyan tablet (Red and blue) and the other two you get by waiting in the boss fight with Kathrin. (Green and yellow)
you can only get one at a time. Its based on the last color generated by Laura so the ones your missing are green and blue.
(btw, There's also one pin your missing if your intending on going back. you get those by dying.)