Hi Dandelion
To me spotting is actual blood, whether it be brown or red. Yellow or other staining I always disregard if I have no other symptoms - but I'm not you and I'm post-menopausal, so it's up to you to decide what to do - we can't really say in this particular instance.
If you don't think it's even enough to call spotting, and you don't think it's an infection - ie if you're not experiencing discomfort, odour or other symptoms, and you are not worried about it, then wait to mention it to your doctor - but keep a note of what it's like and when it happens, but this is your decision, and try not to worry!
Hurdity x