LeonidS, I've tried but failed. How I analysed this using google developer tools to determine what CSS Class was used. Example from the screen dump to your right, The CSS Class is .bx-artificer .col-blue3-dark { }.

The problem that I encountered was, though it works. It changes the color of not only the Sidebar Menu's icon, but also the profile menu's icons on the far left side.

It turned out they are using the same CSS Class.