You can set the font-size and color so that it appears the way you want it to in the HTMLEditor instance window by altering the css (see below) - but this just makes it 'appear' right in that window.
The idea of there being no initial style applied is to ensure that whatever is entered in your editor area (unless you specify a new font-size from the drop-down) will take on the style that you have specified in your stylesheet or in-line css of the containing body, div or span on the page/template that the HTMLEditor entry is output to.
Check the page or template that the Editor code is output to, and set the style for the containing element (body, div, span or email template line) and apply the required style to that element.
If you just want to change the appearance of the (apparent) default style for the Editor input instance, open the Editor stylesheet (webassist/ckeditor/contents.css) and apply those same styles to the body rule - at about line 6)*. That will not change the format of the output, but you will have taken care of that by setting the style of the element that it is output to.
You could also attach your site stylesheet to your HTMLEditor as per my reply to your other post.
* (You may need to clear your browser cache to see the change.)
Could you create and upload a new instance of HTMLEditor on a blank page, and provide a link to it so that we can see what is happening with the return/shift problem?