Add hex input and validation to color picker.

[GreenLightning]

As the title says. Please have a look at the code and tell me what you think.

[ApoorvaJ]

Thanks for your work!

I have made a few review notes on the pull request. Nothing too big, just slight changes to get you used to the code style.

Some comments have gone to "an older commit", but I'm not sure why. You can still view them, though. They are still valid comments.

Please have a look, and I'll merge it in. :)

[GreenLightning]

I amended the commit to fix the things you pointed out. Thanks for pointing stuff out :)

[ApoorvaJ]

Thanks for updating the pull request. Good work! :)