I support the OP and PELaird's suggestion, and not just for notepad.
In Groupy 2 configuration, under tab appearance can I suggest that there is a setting to choose the tab colour of the currently active tab (and as PE Laird suggests).
The 'accessibility' of the fine graduations of colours (or greys) of the different (active and non-active) groupy tabs is not distinguishable by my eyes.
Thanks