"I was specifically replying that what is acceptable at a wedding depends on WHO is wearing it! Pippa is an extreme example to illustrate the point"
Pippa isn't an extreme example of anything.
She was wearing a bridesmaid dress chosen by the bride as bridesmaid dresses often/usually are!
Bridesmaids in white is traditional.
If Op thinks that the bride is likely to be wearing a floral dress then maybe best to avoid.
If it's traditional & bride likely to be in a long plain white/off white dress then no problem.