Hey there,

You can add the following CSS code into Backend > EasySocial > Themes > Custom CSS to change the colour for the 'recent activities' separator:

#es .es-stream-pinned-divider span:before, #es .es-stream-pinned-divider span:after {

    border-top: 1px solid #FF0000;

}

Remember to change the colour code to the colour that you want.

Do take note that remember to clear all your cache before you see the changes.