Possible to determine how many miles on oil visually?

Ok, thanks for that info. If at some point I'm getting the rear main seal done, are there any other seals which should be done at the same time that won't add to much to the labor once everything is opened up?
It's difficult to know since oils darken differently. But paper towel testing it to see if it's extremely brown to black tells you to change it out. If it's darkish brown it's probably fine but close to the end. But broken down oils start to show black or close to on a paper towel. But there's no way to know the life just death. But if unsure just change it.