Formatting a column with hyperlinks (hyperlink column) using JSON

I'm trying to format a hyperlink column but am struggling with the JSON sample provided here:
https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/column-formatting

We have hyperlinks in a custom list. The items are Stable, Low Risk and High Risk and we want to apply RAG colours to those. 

Can anyone supply some JSON? I've spent time trying to figure it but I'm struggling.