Unity UI How to Partially change a texts mask/color by script?

I need to make an Input field which controls/compares the inputed text with a given text and underlines the *characters which do not match*. Just like in Office word it underlines the typos.
I can underline the whole text but i need to find a way to underline only one character.(It doesn't have to be an underline. Might be a mask or even just changing the color of one character would do).
Also i know the way to change the mask or underline some places in text on the inspector but i can't find a way to do it in script.