I’m not exactly sure what you are trying to do, but here are some ideas:

1) You have a task model of all tasks in a table.  Create a 2nd task model that has a condition to show open tasks that are due today or earlier (late.)  Put some red rich text or something annoying across the top of your page “you have late tasks!!”  Set the render condition on the Rich Text to only show up if your late Task model has data rows.

2) You have a task mode of all tasks in a table.  Put a field rendering snippet on a field on the task table that turns the row red if Due Date is today or earlier.
Like this: https://community.skuid.com/t/how-to-highlight-a-table-row-based-on-a-date

3) You have a task model of all tasks in a table. You could show a row action icon (red flag icon, clock icon, as examples) that only appears when Due Date is < TODAY.