Change text on "more" link

How do I change the text of the “more” link which I can manually add into posts by pressing a button on the editor (near where you can select bold, italic etc). In the text editor, this appears as <!–more–> and appears on the post as (more). I would like to change it to say something like Full Details.

The code is buried somewhere in WordPress and I can’t find it. I don’t think it’s my theme (I’m using Supernova) as I’ve been through that code until my eyes went funny.

Other posts say I need to change this line of code:
<?php the_content(__(‘more’));?>
or something similar, but I can’t find this code anywhere.

ALSO, is there anyway of changing the colour of the text “more”. At the moment, it comes up as the standard link colour for the theme.

Please note, this is not the more-tag which is generated by the theme when using excerpts. I’ve found this code in funcions.php and it’s not it.

Thanks for reading my question and thanks in advance for any help you can offer.