Is there a way to make Safari open a dark blank page?
There may be other ways to do this, but a simple way would be to create your own homepage, which could look anyway you like. Then, just set the Homepage in Safari to point at that file.

Make a file called "home.html" with these contents:

&lt;!DOCTYPE html&gt;
&lt;html style="background:#333;"&gt;
&lt;head&gt;
    &lt;title&gt;New Tab&lt;/title&gt;
&lt;/head&gt;
&lt;/html&gt;


Open that file with Safari, and use the preferences dialog to set the homepage to the current page. Also set new tabs and windows to start on your homepage.