We know how to mix colours:
There are three primary colours: red, yellow and blue.
We can mix them to get secondary colours: orange, purple and green.
Red and Yellow will mix to give Orange.
Red and Blue will mix to give Purple.
Blue and Yellow will mix to give Green.
We know this works with paint, but does it work for food dye?
We had three cups of water and three empty cups.
Teacher put a few drops of red food colour into one of the cups of water, blue into another and yellow into another. We used strips of tissue to connect the cups. Look at what happened: the empty cups filled up with water from the cups into which the other end of the tissue went.
We found that red and yellow make orange, red and blue make purple and blue and yellow make green (exactly as we discovered with our paints!)