It turns gray when you have read that chapter and it'll refresh and turn white if you log out of your account or are inactive and have to log into your account again or if you clear your browser history
Mine went gray for a while and then when I went back after a few days, it's not gray anymore TT. I haven't even logged out from my account Gudetama's minion
I don’t remember jack shit, but I do know a hot guy when I see one ٩(๑❛ᴗ❛๑)۶