Wear OS devices operate in two main modes: always-on and active. Take both modes into account when designing watch faces. Generally, if your watch face design looks great in always-on mode with the display dimmed (also known as ambient), it will look even better in active mode with the display fully up and interactive. The opposite is not always true.
When the user moves their wrist to glance at their watch, or touches the display, the screen goes into active mode. Your design can use full color with fluid animation in this mode.
Always-on mode helps the device conserve power. Your design should make clear to the user that the screen is in always-on mode. The background color scheme is limited to black, white, and grays. Your watch face may use some color elements on screens that support it if it is clear that the device is in always-on mode. As a rule of thumb, use color elements for up to 5% of total pixels. In this mode, the screen is only updated once every minute. Only show hours and minutes in always-on mode; do not show seconds, it will look like time has stopped. A notification appears on the watch face when the device switches to always-on mode.