Re: [PATCH 5/7] parse_color: support 24-bit RGB values

Some terminals (like XTerm) allow full 24-bit RGB color
specifications using an extension to the regular ANSI color
scheme. Let's allow users to specify hex RGB colors,
enabling the all-important feature of hot pink ref
decorations:

  git log --format="%h%C(#ff69b4)%d%C(reset) %s"

Signed-off-by: Jeff King <redacted>
---
Also no clue on which terminals support it. I did all of my testing on
a recent version of XTerm. It looks like it doesn't provide true 24-bit
support, though. It is happy to accept the 24-bit colors, but if you do:

  for b in $(seq 255); do
    h=$(printf %02x $b)
    git --no-pager log -1 --format="%C(#0000$h)$b%C(reset)"
  done

the gradient seems to "jump" in discrete steps. That's fine, though.
It's a quality-of-implementation issue for the terminal, and I still
think that the RGB spec is way more readable than the 256-color mode
ones.

 Documentation/config.txt |  3 ++-
 color.c                  | 29 ++++++++++++++++++++++++++++-
 color.h                  |  6 +++---
 t/t4026-color.sh         |  4 ++++
 4 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index f615a5c..a237b82 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -842,7 +842,8 @@ doesn't matter.
 +
 Colors (foreground and background) may also be given as numbers between
 0 and 255; these use ANSI 256-color mode (but note that not all
-terminals may support this).
+terminals may support this).  If your terminal supports it, you may also
+specify 24-bit RGB values as hex, like `#ff0ab3`.
 
 color.diff::
 	Whether to use ANSI escape sequences to add color to patches.

diff --git a/color.c b/color.c
index 6edbcae..78cdbed 100644
--- a/color.c
+++ b/color.c

@@ -32,10 +32,13 @@ struct color {
 		COLOR_UNSPECIFIED = 0,
 		COLOR_NORMAL,
 		COLOR_ANSI, /* basic 0-7 ANSI colors */
-		COLOR_256
+		COLOR_256,
+		COLOR_RGB
 	} state;
 	/* The numeric value for ANSI and 256-color modes */
 	unsigned char value;
+	/* 24-bit RGB color values */
+	unsigned char red, green, blue;