color of heart rate on Apple Watch during fitness session
during workout sessions the color of the heart rate measured change from white to red; it can be white at 115 and red at 105 or viceversa. what's the meaning of the colors?
Apple Watch
You are most likely turning the digital crown.
Turning he crown while in a workout will highlight different metrics.
From pulse, distance, time etc
see Track your progress
When you run or walk, your Apple Watch taps you every mile or
kilometer, and it shows you an update on the screen. If you're cycling,
your Apple Watch taps you every five miles or kilometers instead.1