Shop has a green color selected as background color for buttons, but the Tint color, which is currently a light white, was being used as the background color for the buttons here on the app. After changing the Tint Color to match the background color, the button background updated to match.
First screenshot has Tint Color as a light white color.
First screenshot has Tint Color as a green color, saved on Mobile App tab, under Look and Feel.
This button should be using the background color, not the tint color.