In the Appian User Interface, I have a grid with colored rows. My requirement is that when I click on 'Export to Excel' from the grid, the downloaded Excel file should retain the same row colors. How can I achieve this?

Appian's default Excel export doesn’t preserve grid row colors. To achieve this, use the "Export Data Store Entity to Excel" Smart Service with a pre-styled Excel template. Prepare your data in a Data Store Entity, define colors/styles in the template, and map them during export.

https://docs.appian.com/suite/help/24.4/Export_To_Excel_Smart_Service.html
https://docs.appian.com/suite/help/24.4/Export_To_Excel_Smart_Service.html#exporting-data-to-a-formatted-excel-sheet

As mentioned in your link, I believe the Export DSE to Excel Node will actually overwrite the formatting in any cells that it's used to add data to (and that's beyond how much of a pain it is to create a copy of your template file first so you don't accidentally overwrite it, since they never added a Base Template option).

I think OP might need to try with the JSON to Excel smart service or one of the deprecated Excel Tools smart services (CDT to Excel or SQL to Excel), though these merely don't overwrite formatting, but nothing I know of really allows addition of dynamic formatting.

As mentioned in your link, I believe the Export DSE to Excel Node will actually overwrite the formatting in any cells that it's used to add data to (and that's beyond how much of a pain it is to create a copy of your template file first so you don't accidentally overwrite it, since they never added a Base Template option).

I think OP might need to try with the JSON to Excel smart service or one of the deprecated Excel Tools smart services (CDT to Excel or SQL to Excel), though these merely don't overwrite formatting, but nothing I know of really allows addition of dynamic formatting.