I think it's totally unreasonable to stipulate bra colour - which proves that "they" too deem them see-through which is also inappropriate. Have you spoken to HR about it?
I am assuming that the mens uniforms also include see through shirts. This really is unacceptable and if that was me I would be on the phone to my union. You should not have to wear particular underwear to make the uniform inflicted on you decent. Hopefully the men won't be too thrilled at being made to look daft as well. Of course if they don't have a see through shirt to wear then there is even more reason to complain.
Depends on the colour of the blouse. If it is white, it will almost certainly be see through to a certain extent in which case a white or nude bra is the only way to go.
the issue with the suggestions provided is, they are differing from the uniform, and, at principle, the uniform as it is, is not appropriate. Also, it may not be all seasonal appropriate, IE in the summer it may be too hot.
In adequate work clothing.. mm this i all i can find that can help