Thank you for reaching out to us.
A stain on colored undergarments does not make a woman
niddah. A stain found via transfer from another surface, such as you describe with the toilet paper, does not make a woman
niddah.
Therefore, based on what you write, the small red stain on the tissue did not make you
niddah.
Learn more about the laws of stains
here.
Please be in touch with any further questions.