Change the mod icon but display just purple

We wanna to change the Icon of the mod which will be shown in the players room, and we follow the guides( ,made a correct path and a correct image, set the “Selected image” to our image, but when i enter the game, the icon of the mod still show as only a strange purple, i checked for a long time but nothong found. I thougt it may be a bug or wrong description in the guides. Can anyone know how to deal with this?