All the control surfaces / app buttons in our app use your Shopify Plus checkout branding options to ensure a seamless integrated design. You can customise all buttons in the checkout through the standard Shopify checkout settings.
Log into your Store Admin
Navigate to Online Store > Themes > Customize
Select Checkout from the dropdown at the top of the page
Click the Settings icon on the left - you can manage all your checkout branding here
Scroll down to the Colours section to make your changes