Changing colour of Map pins based on values collected from a form

[JohnW1]

Hi all, 

I'm creating an app that can collect data on Yields of Seaweed Lines. The app has a map interface  which displays the location of each Seaweed Line.

There is also a data entry form which simply records the yield of each line which can be viewed in the App.

I want to change the individual Map icon colours to represent three categories. Either High (Green), Medium (Amber) or Low (red). When I record the yield i want the app to assign a colour to the corresponding points on the map. Could Anyone help me with a solution ?