Placing down / finding an end gateway / end portal and placing down transparent blocks, then looking through the end portal / end gateway on those blocks will make some parts of the block still be visible (e.g. in the case of glass, the white non-transparent parts) through the end portal / end gateway. This only happens when it's in the same chunk as the portal tho. The attachment shows it in the case of an end gateway in front of water and glass.