Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign $DNA$ in addition to a selectable marker?

(N/A) reporter enzyme is used to monitor the transformation of host cells by tracking the activity of its corresponding gene.
For example,the enzyme $\beta$-galactosidase $(LacZ)$ is used in blue-white screening.
When a foreign $DNA$ fragment is inserted into the $LacZ$ gene,the gene becomes inactivated (insertional inactivation).
Consequently,the transformed cells do not produce $\beta$-galactosidase and appear white in the presence of a chromogenic substrate.
In contrast,non-transformed cells or cells with non-recombinant plasmids produce the enzyme and appear blue.