Nesting set inside ifset

[tealborder]

My php file I pass a variable such as:

$userTheme = 'blueTheme';
'vars' => [$userTheme => true]

Can't seem to do:

@ifset blueTheme {
    @set mainColor #0000ff;
}
@ifset purpleTheme {
    @set mainColor #7a00e1;
}

p {
    background-color: $(mainColor);
}

If I run this, the p background color is always set as the last defined @set mainColor