Apex domains cannot have CNAME records.
Question and response
Question
dig blue. NS
Answer
blue. 5 NS b2.nic.blue.
blue. 5 NS b0.nic.blue.
blue. 5 NS c0.nic.blue.
blue. 5 NS a2.nic.blue.
blue. 5 NS a0.nic.blue.
Authority
The response has no authority records.
Additional
a0.nic.blue. 67874 A 65.22.28.9
a2.nic.blue. 146899 A 65.22.31.9
b0.nic.blue. 147782 A 65.22.29.9
b2.nic.blue. 90486 A 65.22.31.13
c0.nic.blue. 120948 A 65.22.30.9
a0.nic.blue. 67874 AAAA 2a01:8840:1e:0:0:0:0:9
a2.nic.blue. 146899 AAAA 2a01:8840:21:0:0:0:0:9
b0.nic.blue. 147782 AAAA 2a01:8840:1f:0:0:0:0:9
b2.nic.blue. 90486 AAAA 2a01:8840:21:0:0:0:0:13
c0.nic.blue. 120948 AAAA 2a01:8840:20:0:0:0:0:9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0