Is a white nation getting "browned" a bad thing? In almost all cases, the answer is probably yes.
This obviously is not due to skin color in of itself, but the behaviors and belief systems that correlate to skin color. While these correlations are by no means weak, they are far enough from absolute that it would be difficult to convince the general public (myself included) that government endorsed discrimination against citizens solely on the basis of race is justified.
There's still hope though. Possible policies exist that would naturally favor white people while still allowing for outlier minorities to thrive. A few examples are as follows.
1.) Child support should be regressive with respect to income level. In other words, the more you make, the lower percentage you'd pay. This would encourage men with higher incomes (generally whites) to have children. It would also, to a lesser extent, discourage men with lower incomes from doing so. Obviously this favors white folks in terms of birth rates.
2.) Tax credits for having children for mid to higher income people.
3.) Free abortion.
4.) Do away w/ affirmative action.
5.) Do away w/ birth right citizenship. Migrants will have an extremely hard time becoming citizens. This means they won't vote.
There's more I could list, but I'm tired. And before you go "muh political feasibility", consider the political and logistical feasibility of kicking out all non whites.