Why is the most side navigation (dashboards) colored using dark background? It seems to draw much more attention, when colored that way. Is it done for creating some visual hierarchy? To be more separated from the content? What's about side navigation that is done in same colors as the main content? Are there any good articles on this matter overall?
My goto solution is creating the hierarchy by using supporting colors within the brand or product's palette that contrast the content. I'm sure there are examples of successful execution in the same color usage but I'd assume it'd be lesser by current trends.
For similar color, you have to use other "effects" to create a similar hierarchy. It could be through typography, negative space, or borders/lines (I'm not sure how to better say that).
In the flat design trend, I presume it would be much harder to be successful with the lack of depth.