A menopausal woman can still become niddah if she experiences uterine bleeding.
Because the applicator was inserted into the vaginal canal, any stain found on it is treated like a stain on a bedikah and we do not apply the leniencies of stains found externally. Therefore, regardless of size, if the color is problematic, you would be rendered niddah.
However, if you can confirm that the blood was due to trauma to the cervix or the vaginal walls (and not from the uterus), then you would not be rendered niddah. You can have your doctor or a bodeket taharah perform an internal examination and if she can visually ascertain the presence of a wound or irritation of the cervix or vagina, then you may attribute the stains to that source and would not be rendered niddah.
For the future, you should avoid looking at the applicator after you remove it, and rinse it off or discard it without looking.
In general, if uterine bleeding resumes a year or more after menopause, it is advisable to see a physician.
Please feel free to get back to us with any further questions.