You could use Conditional Formatting from Format menu.
Select all cells with dates, select Conditional Formatting from Format menu, in the first box select 'Formula is', paste this formula:
=AND(NOW()-A1>=14,NOW()-A1<=20)
click on Format button and choose a color.

Then click on Add to add condition2, select 'Formula is' and paste this formula:
=NOW()-A1>=21
click on Format button and choose another color.

The cell 'A1' in the formula must be changed with the first date range. If your date range is E2:E10 then A1 must be changed in E2.

Regards,
Antonio