Can you describe your proposed layout in more detail? You can use conditional formats to apply a selected fill color to entire fields to highlight them and you can use calculation fields to change text color but if you want selected blocks of text in the same field to be highlighted different colors, I don't think that can be done.
I want an easy on/off text highlight., but colors other than yellow. Can I make another Text Highlight button in gray?
Entire field fill is cumbersome, and not that versatile in terms of quick on/off action like the Text Highlight button.
Are you trying to highlight portions of text in a field or all the text in a field? You can change the text color of selected text in some cases by using a calculation field in place of the text field used to enter/edit data, but you cannot highlight selected text to custom colors as far as I know--unless some layout themes use a different highlight color...
You could use a Web Viewer with this URL:
"data:text/html," & Substitute ( GetAsCSS ( YourTable::YourField ) ; "#FFFF00" ; "#CCCCCC" )
That way you'll see all highlighted text with grey background.