The color picker dialog doesn't appear on IE8

Example to reproduce:

• Login as a user or admin
• Hover over "Wiki" and click on "Administer Wiki"
• Click on "Presentation"
• Click on "Manage Color Themes"
• Click the Default Theme
• Click "Edit"
• Click on the color palette located on the bottom left corner
• Click on the button with a coloured circle drawn on it

Nothing happens when you click the button, even though on the other browsers the button works. You can change the background color by manually typing the code for the color. I've attached screenshots with the differences between IE8 and IE9 and also the error I get on IE8 when I click the button.

Tested on IE8. Does not reproduce on Chrome 23, Firefox 17 and IE9.