You can format the app blocks using CSS. CSS should be added in Zapiet - Product Options > Settings > Theme customization, under Custom styles.
We pre-filled the Custom styles field with some default CSS which will serve as a starting point for any further customizations.
Change the hexadecimal values to the colors you need.
Should the CSS not be applied, add !important after the hexadecimal value
e.g. fill: #e6017e !important;