You can change the primary button or other aspects of your theme by adding code to the Custom Header of your app. The code in this example can easily be interchanged for a different button or color.
background-color: black !important;
border-color: black !important;
This example uses the primary button and the color black. If you would like to change this, I have selected the portion of code in the image below that you will need to edit.
Changing item colors - Community Discussions / How Do I - Tadabase Community