This option allow the user to select the key color for each group of keys.
There are presets on the bottom toolbar that will select colors for all groups.
Space Between Keys is usually set for the keys with rounded corners, but it can also be set for other keys.
Button Text Size is used in addition to your system iOS Dynamic Type setting to adjust the size of the text on CALC 1 Focused and Formula Calculator and 12CP buttons. Dynamic type will adjust the text size in all of your apps that support dynamic type. In CALC 1 this includes lists, options, and some Form Calculators. The Button Text Size option only adjusts the text in calculator buttons.