List validation based on date calculation

MelissaHuff you can do this by formatting the Action column in the image below (your Column B) in advanced mode with JSON. It checks the Arrival column and if the arrival date is more than 180 days in the future then set the text to 'No Action Required' and the background color to green. Otherwise (i.e it is less than 180 days ahead) then set the text to 'Action Required' and the background color to red. 

The JSON for that example is:

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
  "elmType": "div",
  "txtContent": "=if([$Arrival] > addDays(@now(), 180), 'No Action Required', 'Action Required')",
  "style": {
    "background-color": "=if([$Arrival] > addDays(@now(), 180), 'green', 'red')",
    "color": "white",
    "padding-left": "10px"
  }
}

And this is the result:

Rob
Los Gallardos
Microsoft Power Automate Community Super User.
Principal Consultant, SharePoint and Power Platform WSP Global (and classic 1967 Morris Traveller driver)