Apex domains cannot have CNAME records.
Question and response
Question
dig 43.233.68.in-addr.arpa. NS
Answer
43.233.68.in-addr.arpa. 5 NS sns.hostcolor.net.
43.233.68.in-addr.arpa. 5 NS pns.hostcolor.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0