In this short tutorial you will learn how to enable the grayscale mode of your Apple Watch. It should be noted that this setting can only be activated through the Apple Watch app on the companion (paired) iPhone or iPad.
Open the Apple Watch app and tap on My Watch > General > Accessibility. From this menu, toggle Grayscale option On. The new setting is automatically applied to your Apple Watch.
Grayscale mode is a visual accessibility feature that can help people suffering from color blindness or a particular visual impairment to make a better use Apple's range of device, but nonetheless it remains a cool feature.