Drop the panel-default-text color from the color theme and use the content colors for all panel content, to facilitate contrast

Currently, in the flamingo color theme, it is possible to choose a panel background color as well as a panel-default-text color for the color of the text in panels:

The panel-default-text applies only to the pure text of the panels.
However, there are many many other types of content that can appear as content in panels (e.g. links, forms with buttons, etc). For all these other types of content it is not possible to set the color from the color theme variables (without using the advanced section).

The fact that these other colors are not controllable may result in contrast issues between the configurable panel-bg and the contents of the panel. Thus, the fact that panel-default-text is configurable is largely insufficient.

The objective is to make sure that the user that sets variables in color themes can properly ensure contrast for the color theme they're creating.

For this objective for the panels, there are 2 options:

• provide foreground color configurations for all background colors that are configurable. In this case, it would mean to repeat all variables for the content colors in the panel content color configurations (text, links, wells, buttons, etc.). This would mean a lot of foreground colors for panels.
• only allow to configure the background color (for convenience purposes) but clearly state that the foreground color that would be used for the panel contents is the same as the foreground color used in page content. Choosing a color for panels background that is contrast-compatible with the page content foreground would then be the responsibility of the color theme author, but the promise would be that as long as they do that, the color theme will have proper contrast.

The most reasonable option is the option no 2, which is the one that this ticket proposes. Thus, for coherency, the panel-default-text would need to be removed as it wouldn't bring anything (@text-color would be used instead).