Can't change color of Read Only custom field text

The following code will change my text only if it is not marked read only in my custom form. How can I force the read only text to red using the css override?

frappe.ui.form.on("Document", "onload", function(frm,cdt,cdn) {

Here is the field in color when it is not read only:


Here is the field read only:


Yes this is true, you cannot change the color of readonly fields.

Can it be done with a local app css file?

IDK, you should try.