what I want to do is to change the color of a QTableWidget item, when I hover with the mouse over the item of my QTableWidget.
There are no events based on QTableWidgetItem, but you can do this:

reimplement the mouseMoveEvent() of QTableWidget, you can get the mouse position;
use itemAt() method to get the item under your mouse cursor;
customize your item;

This may simalute what you want.
How to catch mouse over event of QTableWidget item in pyqt?