When burned, hydrogen tends to produce a pale blue flame which is almost invisible if you try to look at it in broad daylight. But if there are any sort of impurities like dust, sodium, etc., in the air, then the flame might look yellowish. However, a hydrogen flame will never produce any kind of smoke if it is pure. You can study more about Hydrogen gas by referring to different study materials available on the Vedantu website and app which will help you to understand this topic better.