Tznius cannot be judged outside of the society’s norms and without relating to the individual wearing it. heavy make up is not tzanua if its eyecatching but certainly what is considered heavy makeup is relative from place to place. you can also have this discussion regarding inappropriate wigs and clothes. the bottom line is to follow your rav and try to go with the spirit as well as the letter of the law and recognise that the standards will differ from community to community and not try to impose your ideas on everyone.
On another note. i know of two girls who were reprimanded for wearing makeup in high school . The irony was that neither one was, they just were naturally blessed and looked really beautiful. the principal could not believe that it was natural. so sometimes all this talk may be a case of sour grapes. one girl was so pretty that short of wearing a burka to cover her from head to toe she was noticeable, and in nondescript clothes without makeup. people sometimes forget that Hashem created women and many times they are very beautiful because that’s how Hashem made them. It’s not an aveira to look good.tzinius is also how you comport yourself etc.