silver init looks up the name of its parent process (or, in older versions, at the value of the SILVER_SHELL environment variable, which you're expected to set to $0, which comes to the same thing) and uses that to decide what type of shell is running.

If the parent process is a login shell (e.g. invoked by /usr/bin/login when you log in on a text console, or by sshd when you log in

This theme must not impact the classic prompt.

Pseudocode:

if is default prompt then
    override default colors