Is a garment considered pure if a trace of seminal fluid is smelled from it, but its substance only becomes visible upon the arrival of the moisture of purifying water?

Perhaps you mean semen, as it has an odor unlike pre-seminal fluid. If you strive to wash your garment from semen and its odor is difficult to remove, then it has become pure. The persistence of its odor does not harm you due to the difficulty of its removal. Khalil al-Maliki said: "And wringing it is not required after the removal of its taste, nor of its color and odor if they are difficult to remove."