You are just entering puberty, so you are still having dry orgasms. Your developing seminal vesicles and prostate gland may be starting to produce semen intermittently. Your testes won't be producing sperms yet though.
What you are releasing from your penis when you are not playing with yourself is precum. This is made by your Cowpers glands and is totally different from semen. It can ooze out when you are having sexual thoughts, even if you don't have an erection.
Semen gets its color from the protein it contains, so it can be clear, milky white or yellowish. It can be runny or thick. All these things are normal.
Sperm are colorless by the way.
Give it time and things will settle down as you get a little older. Meanwhile, if you have no foreskin, use lubrication. Spit, cooking oil, baby oil, hand cream, hair conditioner, vaseline or olive oil are all good lubricants for masturbating with.
Girls also have problems when they hit puberty. Their periods start coming very irregularly and the blood volume lost during menstruation can vary enormously.