See attached sample. I Include the exe file.
I have the code you suggested in T716346/how-to-work-with-rich-formatted-content ticket in a button in the toolbar with caption 'Test RTF Cell' in the home Tab.
If pressed it creates the format RTF cell.
However if you double click the cell the red font is lost.
Also in any cell you can format from the toolbar the font attributes e.g. font, font size, weight, style but the font color cannot be changed from the toolbar.