Polygon pixel value scaled



My purpose is to help farmers see variance in their fields in order to improve yield and save money
The idea is that we approach each polygon (different field) differently and stretch the colored scale between the min and max values (pixel NDVI value) of each polygon
In the future I will want to add same scale for the same crop in order to compare to two or more fields or different dates but that can wait

The idea is to use red-yellow-green-blue scale to emphasis the variance

I’m adding 2 pic I took from commercial companies as an example

Can you help me ?