Set your accent color (Design > Brand) and Smart does the rest by generating color palettes for dark and light mode.
This means that you can instantly change the entire look of your site simply by changing the accent color.
High saturation, mid-brightness colors work best. The accent color is intended for the light mode (a brighter version is generated for dark mode). While future improvements will improve the accessibility of colors, not all colors may meet WCAG contrast ratios.