Request for better error message(s)

[CAYdenberg]

If you pass an invalid color into invert you get

Uncaught TypeError: Cannot read property 'r' of null

which is hard to interpret, and doesn't give you much clue that the error is occurring in this package.

I'd be happy to contribute a PR if you're likely to merge it.

[onury]

You're very welcome to send a PR.

If you ask me; the only line with a .r is within toRGB() method. I'd validate the c argument and throw "Invalid color value."

[onury]

v1.2.3 is released.