This bug has not been updated in the last 3 months. Resetting the assignee field.
Please, feel free to pick it up again and add a comment outlining your plans for it if you do still intend to work on it.
This is just trying to clean our backlog of bugs and make bugs available for people.

Hello! I'm a web developer that uses the Firefox inspector every day and I'm interested in working on this issue.

I've read some guides on how to contribute to Mozilla, as I've never contributed before, so I'll need some guidance. But I'm willing to volunteer and learn along the process.

So, this bug would be mostly about reapplying the patch in Bug 1332091 and making it conform to the mockups. We had added the Color Value input before inside a temporary ColorWidget, but later removed it since we didn't have enough resources to bring it into completion. The most of the files in the patch are still relevant except for the ColorWidget files which can be matched to:
https://searchfox.org/mozilla-central/source/devtools/client/shared/widgets/Spectrum.js
https://searchfox.org/mozilla-central/source/devtools/client/shared/widgets/spectrum.css