Some templates use dark colours or background images to style the site, and in some instances this can result in the text of an article becoming unreadable during editing.
A simple and quick fix can be implemented by the editor, forcing the editor text color to black, the editor background to white and the editor text alignment to left.
In the JCE Control Panel, click on the Editor Global Configuraiton button.
Set the High Contrast Mode option to Auto or Yes.
When the option is set to Auto, the editor will determine whether the body text color and background colour provide a workable contrast, and if they don't, will apply the high contrast mode. If the option is set to Yes, the mode is always applied.