Raspberry Pi - strange icon in top right of screen

I have been working with a mobile Raspberry Pi project powered by a LiPo battery and a Powerboost 1000c charger from Adafruit to handle battery charging.

Several times I have seen a small square icon in the top right of the attached small HDMI screen that has a rainbow of colors. I had absolutely no idea where this came from or what it represented.

But now I do... https://www.raspberrypi.org/forums/viewtopic.php?t=82373

The B+ (and presumably later models) has an under-voltage trigger that shows itself as this 'rainbow' square in the top right of the display when the supply voltage drops below 4.65V.

In addition, an over-temperature trigger displays a solid red square in the same location if the temperature goes above 85deg C.

You can disable the warnings in config.txt - see the link for details

I'm glad that the system has these triggers but I don't think the display of a red/rainbow square is a good way to inform the user.