Glazed Terracotta not detectable by commands

When I use the Command: "/execute @a ~~~ detect ~ ~-0.1 ~ Purple_glazed_Terracotta 7 Tp @s ~~~1" It Says: "Failed to execute command 'teleport' as "(player). I have tried this with other glazed terracotta without success. I have tested this with grass and stained_glass and it does work.