A rainbow colored square at the upper-right corner of the screen indicates an under-voltage condition. It’s likely a problem with the power supply and/or the micro USB power cable. Make sure you use a good quality cable and a power supply with proper voltage and amperage output.
There is also a red power LED on the Kwantastic device showing the power level. Under normal condition, the LED is on solid red. If the red LED is off or blinking, you have the a under-voltage condition.