There are browser plugins such as Spectrum [1] that might be more useful.

[1] https://chrome.google.com/webstore/detail/spectrum/ofclemegk...

Last year I wrote a small bookmarklet for doing live, on-site color blindness simulation:

https://github.com/jaz303/ColorScope.js

It's by no means foolproof but I've found it useful for testing sites in development.

upload a screenshot of a webpage?