You generally want to stick to default colors because of terminal color
schemes. If you don't, you risk getting suboptimal contrast and
difficult-to-read text. When you _do_ want to peg something to a color,
you need to fully specify the foreground and background to ensure you
have enough contrast for text to be readable.
Our project, below
(https://github.com/facebookincubator/resctl/tree/master/resctl/below),
wants to set a less jarring highlight color than red. In order to
effectively do this, we need a way to specify the highlighted text color
without causing a cascade of pegged colors. In other words, if we were
to manually set PaletteColor::View, we would need to manually set
everything PaletteColor::View is `ColorStyle`'d with, and so forth.
I realize this is an API breaking change. I spent some time considering
alternatives (such as detecting whether or not `HighlightText` is set,
and if not, use `View` as the highlighted text color). The problem with
the other options is that you'd need to:
1) Document the fallback behavior
2) Maintain backwards compat code paths
Seeing as cursive is pre-1.0 release, I figure this is the best way
forward.
Change the tertiary color in the default theme to white instead of grey.
Currently, the tertiary color is the same as the view background color,
making it invisible as foreground color. This makes the Outset effect
not work as (I think) intended.
This updates `Palette` to add a tree of custom values.
Branches from this tree can be copied back to the root with
Palette::merge. This can be used to group related values together.
