Free tutorials don't cover this stuff because it's not something you can explain in four paragraphs and a few tut photos.
And frankly, most Copic instructors don't understand desaturation well enough to teach it. Ask 'em why some artists use bold violet on faces and you're not likely to get a correct answer.
It's easy to include a gray marker in a free tutorial, especially when you saw someone else use the same recipe and it magically worked for them. So why not pass it on in your blog readers too?
It's much harder to explain why it works or to give readers advice on other similarly effective colors.
A student asked me what Copic Markers I use most
Here's the list.
Not what you expected, eh?
You would never know from this list that red is my favorite color. You can't tell that BG11 appears in almost all my color palettes or that I go through YG03 like it's water. And my list here isn't muted because I only draw and color drab or uninteresting things. I use these markers on everything from freelance human anatomy and technical illustrations to my hobby botanicals.
And yet, these are the markers that sit in little mug on my desk. They rarely go back into my marker storage unit. There's no point in putting away something I'm going to use again soon.
My most used markers won't win any beauty contests. Thhey're not the stars of the show but they are the supporting cast of every image that I color. Every single one.
I use this weird raggle-taggle group of ugly markers to push the beauty queen colors deeper, farther, and stronger. These are the colors I use to create dimension. I don't use them to color, I use them to color my colors.
And I can teach you too.