Changing exported excel sheet cell colour according to its value

There is no out of the box functionality to do this.

In the excel template you should configure Conditional Formatting conditions. You can find many helpful articles or videos to configure it and its pretty simple as well. Then this template should be populated with data as generally done in process models. Excel will take care of color codes as per the conditional formatting configured. I have implemented it in past in my assignments. So give it a try and if you face any issues you can check back here. Hope it helps!