choroba will likely come along with some more details for you, but maybe this will suffice for now, given:

$mw->after( 'idle',
    [ configure => $styleref_select_parent, -background => 'cyan' ],
);
[download]

Even though it could be made more clear, we do see in the Internal Details documentation:

$time is the string 'idle', representing an idle queue timer, or a integer millisecond value.

If you never wanted to use that idle string anomaly, there is an ->afterIdle method. The equivalent of the above could be coded:

$mw->afterIdle([ configure => $styleref_select_parent, -background => 
+'cyan' ]);
[download]

The See Also links to Tk::callbacks where it shows the valid ways to specify a callback, one of which is:

[ 'methodname', args... ], ...
[download]

So going back to the sample from Khen1950fx, we see that he passes 'configure', as the method name, and $styleref_select_parent as the object reference that will be passed as the first argument to Tk::ItemStyle::configure, along with the with arguments to change the background color. Incidentally, the fact that after() method is attached to the "$mw" object means that the timer will be cancelled if the MainWindow is destroyed before it fires.

Here's one last example, that shows the square brackets turn out to be optional in this case, as well. After two seconds, set the entire background color:

$mw->after( 2000 => configure => $tree, -background => 'green' );
[download]