If it's purple.
Yes.
It is possible to transmit HPV via semen.
Doesn't matter what position you are in as long as the semen goes into the vagina.
It is possible for people to be allergic to semen. - Perhaps that is the cause.
It could mean that there is a low quantity of sperm cells in the semen. Or it could mean that the semen was exposed to air, as semen gets thinner within a few minutes.
NO.
as soon as possible
Not unless you rub in some semen.
yes
It's possible that someone with a very keen nose could tell. But you can easily have a drink of something else that will disguise the scent.
Eat a lot of celery. It boosts the amount of semen that you'll produce resulting in a 'bigger' cumshot.
It will not hurt you, but it is a bit of an odd thing to do and remember it is possible to catch STD's from other peoples semen.