If Statement based on % Measure

Neil_Cooper , This seems like a running total % , for that you need a unique column like the index column

If this does not help
Can you share sample data and sample output in table format? Or a sample pbix after removing sensitive data.

Rank with tie breaker can help

%  total = divide([Rank], count(allselected(Table)) )

Then you can have measure like

Switch( true(),

[% total] <= .05,  "Green",

[% total] <= .20,  "Yellow",

"Red"

)

You can use that in conditional formatting using field value option

Rank Tie breaker
https://community.powerbi.com/t5/Community-Blog/Breaking-Ties-in-Rankings-with-RANKX-Using-Multiple-Columns/ba-p/918655
https://databear.com/how-to-use-the-dax-rankx-function-in-power-bi/

Refer this for similar example

https://exceleratorbi.com.au/pareto-analysis-in-power-bi/

For color

How to do conditional formatting by measure and apply it on pie?
https://www.youtube.com/watch?v=RqBb5eBf_I4&list=PLPaNVDMhUXGYo50Ajmr4SgSV9HIQLxc8L
https://community.powerbi.com/t5/Community-Blog/Power-BI-Conditional-formatting-the-Pie-Visual/ba-p/1682539