Improve footer copy on color picker BottomSheet

[iamthomasbishop]

Describe the bug

We've heard that some users assume that the "Select a color" label is an action button. I believe we should phrase this slightly more clearly and potentially change what is displayed depending on whether or not the user has a color selected.

To Reproduce

Steps to reproduce the behavior:

1. Add any block that supports colors (paragraph, button, group, etc)
2. Open the block's settings by tapping on the settings/cog icon near the block's content
3. Tap on one of the color setting cells (i.e. text color or background color)
4. Notice that the footer of the BottomSheet has a text label that says "Select a color" (this is where the confusion arises)

Proposed solution(s)

I propose that we change the label to “Select a color above” (other options considered were "Select color above", "No color selected"). This should be a bit clearer, as it directs users to the color-selection control.

We're also not displaying the selected color's hex value (like we are on the "custom color" picker — in monospace font and the ability to long-press to copy the associated hex value) when the user has a color selected, but it would be good to do so; both for consistency and visibility.

Here's an overview of the interaction:

[enejb]

Great work! I think this makes things cleared.

I wonder if we should display the value next to the colour and if the user clicks on it we can copy it to the clip board. With a little copied tooltip.

And if a user has a colour in the clipboard we could make the copied colour as of the colour that is available to be selected. (maybe even the first one)

I think that would help address some of the issues faced in #3775 issue.