Ah, interesting question... Not many people will be able to answer this. This can be any number of things, without more symptoms it will be difficult for me to narrow it down, but hopefully this helps:
- your semen (which you ejaculate) is a combination of two things. Seminal fluid... (clear/white liquid), and sperm (the little guys that swim around... These guys are actually yellow.) .. Some men encouter times when they have yellow clumps in their semen.. (after not ejaculating for a while).. This is the little spermies. It can have a gel-like texture.
If you're having a yellow pigmentation to your whole ejaculant. This is usually caused by excess riboflavin in your body... (aka vitamin b2).
If you are experiencing both yellow semen and painful ejaculation then you likely have chlamydia. This will cause inflammation of your urinary pipe and from the tube connecting your testicles to your prostate gland---in some men resulting in yellow semen. (apparently gonorrhea can cause this too, but I have never read the medical journals to back this claim up.)