Fix color-shifting bug

[dgant]

Fixes #52 -- see screenshots and explanation there

[JasperGeurtz]

Thank you for the extensive explanation!

Fix is perfect 👍 , maybe char could be used which is unsigned byte in java, but int is good enough because space used is very small + makes code more readable

[Bytekeeper]

Actually, byte should be ok. It's just that you need to "&0xFF" in places were it gets converted to int. Otherwise all values > 128 are negative and will stay negative after the conversion.

[dgant]

Could be made to work, but the overall memory usage is pretty low. short would be a compromise option.

[Bytekeeper]

It's fine. If memory consumption was problem here byte should be the choice. But for "this" int is probably ok. It's also Java, people expect high mem consumption ;)