Yes, there isn't any need to draw any sort of surface details / patterns (stripes, fur color, etc.) in your DaB drawings. In fact, it's actually better to avoid adding details like that entirely, as they will likely obfuscate or distract from the underlying construction.

It's important to remember that details are just details: the underlying construction is the most important element in DaB drawings. Without that, no amount of extra details will make the drawing look more believable or 3D.

IIRC Uncomfortable requests students to do a certain number of drawings for the homework assignment without adding any detail whatsoever. That is likely due to what I stated above (and a few other things, but that's the main gist of it lol)

Hopefully that answers your question :-)