Highlight letters on touch

I am working on a puzzle game, I am wondering how to highlight words just like in this photo? I am already able to detect letters throught touch and even can form a word but i just want to add highlight on it. Thank you so much.

I just started selling a template for making work search games.  You might be interested in this post: https://forums.coronalabs.com/topic/73269-try-before-you-buy-game-starters-word-snap-word-search/

I just started selling a template for making work search games.  You might be interested in this post: https://forums.coronalabs.com/topic/73269-try-before-you-buy-game-starters-word-snap-word-search/