If the stain was found on a colored garment, it may be disregarded and did not render you niddah.

If the stain was found on a white garment, and the stain was clearly reddish, your status depends on the size of the stain. You can try comparing it to a coin the size of a gris (the area of a circle about 19 millimeters in diameter), such as a US dime or Israeli shekel.

If you are still unsure whether the stain rendered you niddah, if you have any real doubt about the stain's origin (it may be an old stain that you just noticed now, you may have eaten something reddish that spilled on your pants, etc.) you may disregard the stain.

Only if the stain was found on a white surface, was clearly reddish and larger than a gris, and you have no alternative source to attribute it to, then it would render you niddah. You would be required to wait the minimum days before performing a hefsek taharah, counting the seven clean days, and immersing in a mikveh.

If the color and/or size of the stain are questionable, it would need evaluation by a halachic authority. Unfortunately, cameras generally do not capture color with anything close to the accuracy necessary for a halachic ruling. Therefore, stains should be evaluated in person and not via a photograph. However, in situations like yours, where a woman does not have access to a halachic authority, we recommend the Tahor App. This app uses sophisticated color calibration technology to take a picture of a stain& or bedikah and send it to a Rabbi for evaluation. The app instructs the user to place a coin next to the stain, which enables the Rabbi to evaluate the size as well. Please note that, as of this writing, the app is available for the iPhone and for a few models of Android phones.

Please feel free to get back to us with any further questions.

B'hatzlacha!