What happened to the urine line of diapers? Replace it?

There's no need to change color every time. The color change is to remind you that you have urine. But if you don't feel much urine, you can continue to use it. If you feel that the diaper is heavy, you should change it. So some diapers have urine display tips, but many diapers don't, because there is no need to look at the display tips. The best way is to touch it and feel if there is much urine.