Pink and Black Checkerboard Clay?

So I'm using the /fill command to make a roof for a shop, and I type:
/fill x1 y1 z1 x2 y2 z2 Clay 6
whilst attempting to make a roof of pink stained clay. Instead, I get pink and black checkerboard blocks. (Same thing happens no matter what number I put at the end, granted I put a positive integer less than 16.)
I thought at first that I should put hardened_clay instead of Clay, and the same thing happens. Finally, after consulting the wiki, I found out that the correct usage is Stained_Hardened_Clay. So now that I've got my clay, is the checkerboard block supposed to be like that?
Attached is a picture of the building with the checkerboard roof.
EDIT: I guess users didn't get what I was aiming at with this. My point wasn't that the /fill command wasn't working, my point was that the checkerboard clay was appearing for all numbers, when those data values don't even exist.