Test-tubes P and Q were each filled with a solution of red hydrogencarbonate indicator. Hydrogencarbonate indicator turns yellow when the carbon dioxide concentration increases and turns purple when the carbon dioxide concentration decreases. Equal pieces of the same aquatic plant were placed in tubes P and Q. Tube P was left uncovered, while tube Q was covered with a black light-proof cover. The tubes were kept for four hours in a warm room in sunlight. What would be the colour of the hydrogencarbonate indicator in the two tubes after four hours?