highlighting effect in read aloud

[me too]

hello all
i had created an epub3 with read aloud feature,as i had opened it on readium i found it working well,it has also a hightiting phenomenonn (highlights each word as it sounds),but i would like to do it different,as changing the background image (yellow color in attached files)as it procceds reading,i have something like that did using the language C,but it is not helpful. i have an attachment with a print sreen in which the feature is displayed.
i am running out of ideas
any help would be appreciated
thank you in advance