diff% error

My understanding is that the `diff% `in the test results refer to the percentage of difference between the ref and test. When I set the `"misMatchThreshold" : 20`, differences higher than 20% will fail the test.

But when I compared 2 completely different websites, I'm not getting `diff%` of 100. It's showing diff% of around 30 when the websites are totally different.

In other words, diff% is never 100% even if it's comparing a black background with a white background.

Bug or I'm missing something?

Thanks.