How to change the forecolor of WPF datagrid cells and rows if its text is changed?

I'm using Prism and VS2012, i'd like to have a DataGrid which has following behaviors:

1. if the text of a cell is updated, then the foreground color of textblock in this cell will be changed, e.g. in Blue.

2. if a new record is added to this DataGrid, the new row will be shown as in blue as well.

3. After Save command executed, all these blue cells and rows should be turn in black.

May i know what should be the best practice to implement these in xaml and MVVM?

Thank you.