I believe either the "sailor(s)" interviewed for that documentary were incorrect or the original poster misinterpreted what they said. Those were not colored smoke rounds, but were shells that contained a colored dye. With multiple friendly
ships often targeting the same enemy ship, the use of different colored dye rounds enabled the gunners/fire control
officers to determine where -their- round(s) were falling.
If they had used "colored smoke" rounds, the resultant obscuration would not be useful.
Regards, Odd