Hi there ~
Orange spots in underwear can be many things and one of the most important issues is the fact the your husband may be dehydrated. It could also be that you are overreacting to a certain color compared with another. If you are suspicious about your husband's sexual activity please consult a psychiatrist
or use marital counselors who can help you with the same. However, it might be better first to discuss it with your husband. I hope this helps.
Take care and have a lovely day!