I have never worn or asked anybody to wear anything because of scrapping purposes. But Have been known to add accessories to a picture area to help make it more matchable or different than other similar photos. Like one Christmas, helping my Mom set up tables and get ready for company the next day, I asked if she would use her Chrystal candle holders for the Buffet table because I had paper that matched the design in the candle holders. My Mom was an awesome Mom so she said sure! Or have somebody hold a 7Up drink instead of other soda for the color of the can. I mean it's not like anybody is doing a bad thing by making requests for scrap purposes...we could have much worse things in our pasts than having the kids wear matching shirts!!
I think it is pretty awesome that so many of us have a plan of what we need or want before the pics even get taken!! Way to Go! Good Planning is a Wonderful Quality for many jobs and life in general so I think You all deserve a pat on the back for your efforts!!
Carry On and Keep up the Good Work!!