Add a feature to set alpha value to Highlight

[shimotmk]

What?

fix #67453

Add a feature to set alpha value to Highlight

Why?

Being able to set alpha color expands the range of design possibilities!

How?

Testing Instructions

1. Open a post or page.
2. Insert a paragraph block.
3. Set Highlight text or background alpha color

Testing Instructions for Keyboard

Screenshots or screencast

textcoloralpha.mp4

Before	After

[github-actions]

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Co-authored-by: shimotmk <[email protected]>
Co-authored-by: t-hamano <[email protected]>
Co-authored-by: hanneslsm <[email protected]>

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[shimotmk]

Could someone please take a look at this pull request? 🙂

[t-hamano]

Sorry for the late reply.

This feature works well and I think it's ready to ship. I think it's very useful when you want to apply a soft background color that blends in a bit with the text:

I re-read #34680 where the background color feature was implemented, but there was no specific mention of any concerns about adding alpha color.

One thing to note is that alpha color will be available for both text color and background color.

I believe this is a very important change and would like to solicit additional feedback. cc @WordPress/gutenberg-core

[shimotmk]

It's been about a month.
The color of block supports can be set to alpha color.
I'd like to get some design feedback and move forward.

Color	Background

[hanneslsm]

I'd like to get some design feedback and move forward.

What design feedback is exactly needed?
I think this looks visually fine.