Variable colourful according to the water temperature

This is safety instruction to avoiding hurt by the very cold and very hot water

There are 3 colours, blue, green and red. 
1.When water is 0-30 degree centidegree, the colour is blue
2.when water is 31-40 degree centidegree, the colour is green
3.when water is above 41 degree centidegree, the colour is red