Change color in one column based on value in other column

wqhlmethis What is the data type of Completed column?

If data type of completed column is Yes/No, use this JSON for due date: 

{
    "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
    "elmType": "div",
    "txtContent": "@currentField",
    "style": {
        "background-color": "=if([$COMPLETED], '', if((@currentField <= @now + 86400000), 'red', if((@currentField >= @now + 86400000 && @currentField <= @now + 345600000),'orange','')))"
    }
}

If data type of completed column is single line of text or choice, use this JSON for due date: 

{
    "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
    "elmType": "div",
    "txtContent": "@currentField",
    "style": {
        "background-color": "=if([$COMPLETED] == 'Yes', '', if((@currentField <= @now + 86400000), 'red', if((@currentField >= @now + 86400000 && @currentField <= @now + 345600000),'orange','')))"
    }
}

 Note: Make sure you are using correct internal name of completed column in JSON. Follow this article to get internal name of your SharePoint column: How to find the Internal name of columns in SharePoint Online? 

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