Problem with hexadecimal #000000

[Daniel4Digital]

Hi there,

When I try to do a difference between any color and #000000 it gives NaN and not the actual difference.

[Daniel4Digital]

The same with FFFFFF. It gives NaN.

difference('#1E1E1E', '#FFFFFF')
difference('#1E1E1E', '#000000')

[e-domnenko]

PR #52 fixes this issue.