Step 1: There are only three termination codons in the standard genetic code, and none of them specify an amino acid.
Step 2: Geneticists in the 1960s named these codons after colors to tell them apart in discussions: UAG was named amber, UGA became opal, and UAA became ochre.
Step 3: AUG is the initiation codon and also codes for internal methionine residues, so it cannot be a stop codon.
Matching the nickname to the codon gives UAA = ochre.