Thank you for your answer, but that is not the question.
The issue is that even if I select the Header and Sidebar Background Color in Dashboard->Apperance->Customize->Colors, that color isn’t rendered!, the background color in header or sidebar I see is the main background color. So, adding the !important rule to CSS, browsers render the background color I selected ok.
The expected behaviour is ok while you’re in customize screen and change the colors but when you save the changes and visit the blog, the issue happens.