Shape map - gradient color

Hello,

I create a shape map which use self define map ( .json). Shape map shows % covering of ( water, forest, road, house) in cities of a country. The  covering of water is from 50-70% and the  covering of road is for 0,5-3,5 %. It leads to at the color does not shows  the differences between districts if I choose the min color  is 0 and max is ( for example 80%)! 

My problem are:

how can i set the minimum and maximum at gradient color which change automaic whith the change og filter ( water, forest, road, house)?. 

Thank you!