Thanks for bringing this concern to my attention, @PS-0401. No worries I've got you covered. I'm here to help you change and add colors to your invoices. 

If you create a design using the Customize Design feature, you can customize the design and change the color of your invoice. However, it's important to note that the colors available when customizing this new design will differ from those found in the latter feature and can't be reverted.

I recommend creating a new design and copying it first to have a second copy of your template before changing the colors in it. This way, you still have the original copy of the design and the new ones. 

Here's how:

1. Create or open an invoice.
2. Click on the Customize Design dropdown, then select Customize Design.
3. Follow the onscreen steps to customize the templates, then click NEXT.
4. Put a check on the sales forms you want the new design to be applied, then click Apply.
5. Click OK, then Save.
6. Go back to the invoice, then click on Manage Templates.
7. Select the template you want to copy, then click the Copy button.
8. Click OK.
9. Under the Select Color scheme dropdown, select a color you want to add, then click Apply Color Scheme.
10. Select OK to save the changes.

Additionally, if you encounter issues when using or customizing templates, you can fix these common template issues in QuickBooks Desktop. 

Keep me posted if you need further assistance in customizing your invoice templates. I'm here to help you out in any way possible. Have a great day ahead and stay safe!