I don’t know about such tutorial, sorry, but …

on the Digitone you are on a FM synthesizer and I would recommend to spend some time exploring how to create very different FM sounds.

It’s not as direct and IMO easy as using the typical MiniMoog like instrument with subtractive synthesis, but it isn’t witch-craft either. Just a complete different approach. FM is well known for providing the most different timbres with two or more operators.

If you are interested in FM synthesis basics, you could start with this ancient article by Sound On Sound magazine

You don’t even need to understand the “maths” of this article to get your head around, what concepts lead to which sounds - basically.

The design of the DN takes a lot of this math away and supports direct twiggling of knobs and quite easy success.

Maybe you could describe your “brown sounds” and what you up to achieve?