An active state shows an item while someone is pressing it or using it right now. It is like a doorbell button that dips down while your finger is on it.
On a website, a button may darken briefly when clicked. A navigation item might stay highlighted to show which section is currently open. Those two uses are related, but they communicate different moments.
Make the change noticeable without relying only on color. This feedback helps people understand that their action registered and which part of the site they are viewing.