What? I've formed plenty of countries with colonies and never had more revolts because of it.
I never did Netherlands but I've made UK with England, Spain with Portugal, Italy with Naples and HRE with plenty others, and never had more revolts because I enacted a decision that changed my country.
That is not possibly correct unless you formed the unions when you had no current colonies. If you form a union any province that is currently less than city size will get nationalism revolt risk for your old tag nation. It seems like a bug to me and so may be fixed in the next patch along with settlements in horde territories disappearing when you tag change but in 5.1 you absolutely get rr in colonies when you tag change.