Intellegent, Sorry but you have not defined bright colors. White is the brightest of all. Are you saying it is assur for kallahs to wear white dresses any more? Is this a new halacha or minhag in the Jewish marriage ceremony now?
Since you can’t define it, better not to and leave it to people’s good tastes, rather than legislating some brand new arbitrary guidelines that somebody just made up on the spot and calling it yiddishkeit.
There is no halacha against looking nice or attractive (even niddos are obligated to do so), and the downside is that if frum women are forced to look shlumpy, then their husbands may look elsewhere and cause shalom bayis problems, as gemara says over and over shelo tisganeh al baalah.