First stage was easy - second was easy split the mercury turn one blob red and the other green + yellow blob...open door. Then I sit on the checkered flag and nothing. What do you do after this?
once you opened the gate, you need to mix all 3 colours together (red, blue, yellow) to turn it into the normal default silver merury. (see the silver flag?, it means it needs a silver coloured mercury)
the colour-chart on the top right is a great help for mixing diff. colours.