Right - from memory:
In the room on the far left there's a colour mixing chart on the wall...............pick a colour you want to mix and the two either side of it will result in the colour in the middle when put together.....................SO:
Take a look on the teleport, that's the color you need do mix by mixing up 2 colors.
If you do it wrong it starts back at yellow (for which you click red and green)
Then it will give you another target colour, get this right and you'll get a third, get this right and it should be ready, it goes a sort of grey or white colour when you've done it!