I need to write a script based on the value of a cell in relationship to another cell....

Example:

Day 1. Money total is $40.50
Day 2. Money total is $45.00. So based on this, the value is +$ 4.50 (results in black)

or it could be this;

Day 1. Money total is $75.00
Day 2. Money total is $73.50. So based on this, the value is -$1.50 (which should be in red)

Any help will be appreciated.