Default Settings allow modifying preexisting settings to clients personal preferences. They might be further overwritten by individual country settings.
What is Hex color?
Designers and developers use HEX colors in web design. A HEX color is expressed as a six-digit combination of numbers and letters defined by its mix of red, green and blue (RGB). Basically, a HEX color code is a shorthand for its RGB values with a little conversion gymnastics in between.
Widget accent color
It is the main color that can be adjusted by using the Hex color code. As a separate option accent color can be applied to widget elements like buttons, pins on maps, and radio buttons.
For example, by using #f79323 (orange) as an accent color you can achieve the below look:
Widget effects color
Effects color is for effects like border shadow, radio button when hovered, etc.
Overrides the widget accent color for the progress bar in the Free Delivery Indicator.