The Press This bookmarklet sends you to a page using white text on a white background in Safari. It may seem like it isn’t there, but by selecting the textbox the text in the editor reveals it is functioning properly, whiteness of text aside.
One option is saving as a draft and then going into the admin page and editing it allows you to see the text that wordpress accidentally hides.
A better temporary fix for me is to edit the press-this.php file located in the wp-admin folder. I changed this line:
That means no rich text editor, but I don’t really use that anyway. Besides, it is much more useful to see the text.
see more: WordPress › Support » Press This bug