While I am doing my best to find the best values for the color recognition, every camera is a bit different, which makes it hard to find values that work best on most phones.
You get the best results with a bright background and good lights. On some phones flash/torch helps as well, on some (such as on my Z3 Compact) it makes it even a bit worse.
If you have suggestions regarding the improvement of the recognition process and/or my chosen color bounds, please feel free to let me know by posting in my XDA thread or even issuing a pull request on my GitHub repo (https://github.com/laufersteppenwolf/ScanR).
In order to scan the resistor, place the blue line over the color bands indicating the resistance with the tolerance band to the right, but do not scan the tolerance band as well. Once you've placed the line properly over the resistor, press the scan button.
The app will then record a certain amount of values (can be set via settings) and then get the most popular element. However, if the wrong value got detected, you can simply edit it yourself from within the result screen.