light, dark, and theme adjustment & generation [was: solarized]

[Drew Adams <drew.adams@oracle.com>]

1. Following on what I said about existing code that
complements colors -

I should be clear that not taking into consideration
human perception, which means also ambient lighting etc.,
a mechanical complementing/inverting function often
results in colors that, while technically complementary
(including saturation and value, not just hue), are
not ideal.

I use color complementing often when I define default
face values for a library.  Since I personally use a
light background (but not too light), with a fair
amount of ambient lighting (e.g. for working also with
paper), I define a face's default color for a light
background, and then I take the complement to get a
default color for a dark background.

I might also quickly check what that looks like, but
I don't really establish a dark setting (ambient
lighting) with a dark background mode to see what the
effect might be.  The result can well be something
that people who do use a dark background might find
less than ideal.  (I leave to them to customize the
face, or submit a suggestion of a better dark default ;-).)

___

2. One thing that I think can help, is being able to
adjust hue, saturation, and value across all faces
at once, to find what one prefers and see which faces
might be outliers.  For example, desaturate all faces,
or increase all their values.

Icicles gives you ways to do that: cycle, incrementing
or decrementing any of hue, value, and saturation.

And you can save any particular appearance you like,
as a color theme or custom theme.

And then you can further tweak individual faces in
your theme, which are unfortunate outliers from the
global change you got to by changing hue, saturation,
and value across all faces together.

I'm not advertising this as an Icicles feature.  My
point is to suggest having tools to globally tweak
an appearance and create a theme from that.  That
includes starting with some theme and tweaking it.

Besides adjusting hue, saturation, and value, it would
be good to be able to adjust _contrast_.

Others have brought up theme generation.  I'm not sure
what was meant by that, but what I describe here could
be considered a kind of theme generation, as well as a
kind of theme editing.

IOW, besides customizing individual face settings in
a theme, it can be quite useful to be able to adjust
a set of faces used by a them _together_.

The Icicles commands that do this act on all faces.
But it could be helpful to be able to (easily, somehow)
limit such global tweaking to a particular subset of
faces.