Changing dataGridView rows by colors depending on time passed by

[fredy21]

There's a homework that has to be done in X weeks from now, for example.
I create a new homework, set the starting date to July 22nd of 2014 and the end date to August 6 of 2014.

I need the row to change in the dataGridView from green, to yellow, to red depending on how close is the end day of the homework.

Let's say, from the starting day to 50% of the time set of the homework, the row stays green. From 50% to 80% the row changes to yellow and from 80% to 100% the row changes to red.