Content controls don't have a background grey colour - other than when selected and showing placeholder text. On Word versions after 2010 they don't need a border; and the placeholder text is optional and/or customisable in all versions.
You might find
https://www.gmayor.com/insert_content_control_addin.htm useful as a simple way of inserting controls (customised as you want) into a repeating content control. (You will have to insert the repeating control itself normally).
If you add a new section in the repeating control, that section's content controls are not filled in from the previous section - at least not here in Word 2016. The table is repeated c/w its controls unfilled.