Tum'ah is not contamination. The main ramification in the time of Beit haMikdash was that anyone who had contact with a niddah would immerse in the mikveh and wait for sunset before offering a sacrifice at the Temple or eating sanctified food. For most women, there would be little or no effect on everyday life. The effects would be more significant for those who ate their everyday, non-sanctified food in a state of taharah (purity), and for the families of kohanim who frequently ate sanctified food.
It is important to remember that there were many sources of tum'ah. Niddah was specific to women; however, some forms of tum'ah were specific to men and many were independent of gender.
The special clothing for a woman during niddah was a necessary measure in those times so that someone heading to the Temple would know to avoid contact with her, or to immerse after contact. It also served as a practical reminder to the couple that relations were prohibited. However, since this was a societal norm and all menstruating women participated in it, married or unmarried, it was presumably taken as a natural part of a woman's life. In our context, since there is no practical need for it, and since unmarried women are always in niddah, it would indeed not be modest to continue with recognizably different clothing.