When you try to change text color, the Variables button disappear.
Steps to reproduce:
1. Go to "Administer Wiki"
2. Go to "Look and feel" panel and then click on Presentation
3. Under title Color Theme, click on "Customize" button.
4. On the left side, click on tab "Logos" and then click on other tab "Base colors"
5. Every tab from the Variables panel disappear one by one after you click on them. (Logos, Base color, Typografy, Buttons, Navigation Bar, Drop downs, Form, Panels, Breadcumb, Advanced)