Thank you for reaching out to us.

Bloody discharge on a bedikah cloth is treated much more stringently than a stain on a garment. For example, on a garment, a stain's size can be a factor for leniency, whereas on a bedikah cloth, a niddah color of any size can make a woman niddah or interrupt her clean days. The key question on a bedikah cloth is whether a given shade is a niddah color, which can sometimes be the case even for a fainter color.

Additionally, there are different received traditions for evaluating cloths passed down from rabbi to student, so that it is possible that this rav follows a different tradition than your former rav. 

All the above notwithstanding, we recommend checking in with your old rav to discuss what types of stains and bedikah cloths you might be able to assess for yourself, based on what you have shown him over the years. We also recommend speaking with the new rav to be able to understand his recent ruling better. This way, you are less likely to be caught by surprise in the future.

You might also find it helpful to see our discussion of evaluating bedikot here.

Please let us know if we can be of further assistance.