How to change the Add to Cart and other Button colors in your theme
Buttons in Pipeline use the Link color value in your theme's color settings:

Use the theme's color settings:

Under General, choose Link color:

Note: If you're using a Modal cart, the pop-up style; the Accent color is used for the button.
Example of Add to Cart button with a blue outline color:

Using a color setting to help make your button stand out better can help with conversion.
Additional button examples
Page Cart button:

Footer newsletter button:
