If the curved "Wi-Fi" bars at the top of your Live View changes color, it's measuring the quality of your device's connection to your Wi-Fi Network. The three colors the bar can turn are:
Green: This indicates that you have a strong connection to the network and should experience no problems using the Live View function.
Yellow: Your network connection is weaker than it should be. You may experience some problems with your Live View.
Red: Your network connection is extremely weak or sporadic. You may experience severe problems including a black screen with your Live View.
An example of such a message can be seen in the image below:
Note that it is possible to see these bars on both the device and your mobile device. Having the bars on the device indicates a weak connection between your device and your router. You may want to check your device's cable or Wi-Fi connection. If the bars are on the mobile device symbol, it indicates your mobile device has a weak connection to the internet. Try moving to a location with a better connection or connect to Wi-Fi.