ActionScript 3.0 :: One Textfield Have Multiple Text Backgrounds?

I have been trying to find a way to color the backgrounds of different words in a single textfield with different colors. 
 
For an example, lets imagine the whole text is a story which has nouns and verbs...etc Now I want to show the full text which is my story and highlight the background of nouns in blue, verbs in red.

Then I have dedicated toggle buttons for each types. The use of those buttons is removing or showing those backgrounds. For an example and when user clicks on noun button it will remove or show the background of all the nouns. Same for the button for verbs.
 
Then you may ask why I can't achieve this by using separate textfield for each word in the story and line them like a paragraph. The problem is user should be able to edit those text. So those are INPUT typed textfields. So all the words should move within the boundaries of paragraph when user keep changing one word. see the second attachment and you may see that I have changed the first word by typing "abcde", so as I type all other words should move like you type inside a textfield. So thats why I think if we can achieve it using single textfield rearranging words as user types is taken care of the textfiled so we don't need to place all the words manually.

When I was trying to think of a way to do it, I found that background is only a property of TextField, but not TextFormat. If it was a property of textformat then I could have set different formats for different words in same textfield. So that option is out.

Also I thought of using CSS with htmlText. But unfortunately text-background is not supported by actionscript stylesheet class.