The air bubble would stand out from the colored water sol. hence it would provide accurate results...it isn't necessary to use coloured water unless you really want that accurate results and slight of simplicity.
Mwelwa Malunga , if it was a glass tube the water will just go out of the open end.(the end which is inserted in the water beaker). if it's a capillary tube, the water will not flow out of that end, even when u lift the open end out of the water beaker. it's a physics related phenomena. Therefore, with the capillary tube, the water cannot flow out through the open end. The only way now, the water can move is in the opposite direction, because the plant is pulling the water up.
