Manually adding hex color in color picker dialog doesn't pre-fill with hashtag when changing table cell border or background

[f1ames]

Are you reporting a feature or a bug?

Feature request

Check if the issue is already reported

Extracted from #565. See also #590.

Provide detailed reproduction steps (if any)

1. Go to http://sdk.ckeditor.com/samples/fullpreset.html.
2. Right click into table cell.
3. Select Cell -> Cell Properties.
4. Press Choose button next to Background Color.
5. Type color value in input field (just above Clear button) in hexadecimal 6-digit format without leading #. E.g. (ABC123).
6. Click OK.
7. Click OK.

Expected result

#ABC123 color was applied as an cell background.

Actual result

No color applied due to invalid hex (ABC123) value.

Other details

• Browser: All
• OS: All
• CKEditor version: 4.7.1
• Installed CKEditor plugins: Full preset

[f1ames]

Closed in #580.