Your customer should understand one big risk of background noise systems. If they ever fail, and the staff suddenly has a quiet background, it can cause all sorts of strife. When open plans included these, they were frequently built with full redundancy and even battery backup. If they do not have one now, and it gets turned on, be ready for complaints. Bring it up very gradually over a week or so.
I am not sure white was what was used. Usually some shaping as it is conversation levels that are to be masked.