bug#24273: 25.1.50; Unexpected return value from `color-name-to-rgb'

[Simen Heggestøyl]

The docstring for `color-name-to-rgb' states the following:

"Normally the return value is a list of three floating-point numbers,
(RED GREEN BLUE), each between 0.0 and 1.0 inclusive."

When passing the hex value for white the return value is as expected:

     (color-name-to-rgb "#ffffff")
          ⇒ (1.0 1.0 1.0)

But when passing the name of the same color, the return value becomes
different:

     (color-name-to-rgb "white")
          ⇒ (1.00390625 1.00390625 1.00390625)


In GNU Emacs 25.1.50.134 (x86_64-pc-linux-gnu, GTK+ Version 3.20.7)
 of 2016-08-20 built on x240
Repository revision: a4ba426d25bd6a5cbe11d81b82a789b8a2c948ed
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:     Debian GNU/Linux testing (stretch)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS NOTIFY GNUTLS LIBXML2
FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr ispell emacsbug message subr-x puny seq byte-opt
gv bytecomp byte-compile cl-extra help-mode cconv cl-loaddefs pcase
cl-lib dired dired-loaddefs format-spec rfc822 mml easymenu mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev obarray minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 99389 6019)
 (symbols 48 20750 0)
 (miscs 40 46 109)
 (strings 32 18640 5788)
 (string-bytes 1 591726)
 (vectors 16 13763)
 (vector-slots 8 450400 3027)
 (floats 8 183 16)
 (intervals 56 195 0)
 (buffers 976 11)
 (heap 1024 35065 1072))