Hi all,
Thanks to @Nived_Nambiar and @v-xiaochen-msft I was able to fix my issue to have past due 'due dates' highlight red in my HTML table that I send via Power Automate each day. Thank you again!
I've identified an additional requirement based on our workflow in that we would also like to have the due date cell highlight yellow (keeping text red) if the due date is more than 5 days past due. I've tried dropping some background-color expressions in my Select action, but am getting errors.

My current if expression is:
if(less(item()?['DueDate'],utcnow()),'red','black')
My convertFromUtc expression is:
convertFromUtc(item()?['DueDate'],'Eastern Standard Time', 'h:mm tt dddd MMMM d, yyyy')
Then I do a Replace expression in the body of the email:
replace(replace(replace(body('Create_HTML_table2'),'<','<'),'>','>'),'"','"')
Which generates:

The dropping of background-color in that I've tried has not worked.
I'm not sure how to combine both the red font and yellow background desire in the Requestor Due Date box in my select action. Can anyone assist?
Thanks in advance!