If the sperm looks slightly yellow in color on white paper, then the possible causes: 1. Patients who have not defecated for a long time, such as in the first defecation can have a slightly yellow semen color, which is a normal physiological phenomenon. As the volume of semen discharge increases and the frequency of defecation increases, their semen can return to grayish white or milky white. This process is not accompanied by any symptoms such as painful ejaculation and pain in the urethra, which is a physiological condition and does not require drug treatment.2. If there is an infection, yellowish semen color can occur, mostly accompanied by painful ejaculation or painful urethra. The infection can be caused by a urinary tract infection or by an infection in the seminal mound or seminal vesicles. When an infection occurs, there can be pus mixed with the semen and yellowish semen color. It is necessary to take the relevant semen for a bacterial culture test to clarify whether there is an infection, and the infecting bacteria is mostly Staphylococcus aureus.