On existing table black text but when adding new column or rows it goes into blue text with an underline.

Your screenshot shows a pink highlight color which indicates a missing font. What paragraph style are you using? Are you using any Cell styles?

In your Character Styles panel, is it selected to None (which is the normal condition) or on a style that calls for blue underline? If so, deselect all text, set the Character style to None. In the affected table, select the blue parts, and click None in the Character Style panel.