Color Picker: Set initial hex value for picker (closes #20326)

[bjarnef]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes #20326

Description

This issue was it set hex value without # in hidden <input type="color" /> - it need to be a hex color with # and 6-digits (3-digits doesn't work to set initial color picker value). The value is still stored as in previous format without #.

Initially most browsers probably set black as default color, so without change color via click, drag or input it doesn't trigger change event, but it's okay although a bit annoying when one wants to select black initially 😅

I also expanded the hex from 3-digits to 6-digits in the local variable, so it works for e.g. #555.

chrome_5olSkQgR3p.mp4

[github-actions]

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[Copilot]

Pull Request Overview

This PR fixes an issue where the hidden color input was not using a valid hex color format, causing browsers to not trigger change events properly. The change ensures the color input receives a properly formatted hex value with the # prefix.

[AndyButland]

Great work, thanks @bjarnef - I've tested out locally and see it working correctly now, for 3 and 6 digit colour values.