the grass in the grass block texture normally becomes snow when snow is put on it but when the grass blocks are generated in the "ice plains" , "cold taiga" and "mountains" biomes the grass blocks keep their normal texture and are not snow-covered
it also appeared during snapshots of the 1.13 a little older (18w07a, 18w08a, 18w08b 18w09a ect...)
Duplicate of [MC-124312]