You can easily change button colors in the Flits Customer Account Page by following steps given below.
Step 1: Open Themes under Online Store section from the left side navigation in Shopify store admin.
Step 2: In the Themes section click the Customize button beside the theme name in which you would like to perform changes.
Step 3 : From the left side navigation, in Theme Settings open App:Flits
Step 4 : In App:Flits you will see Button Names along with Button Colors. From this section, you can select the color of your choice and save it. Refer below images.
If you need any help, drop a mail at firstname.lastname@example.org