succumb to american spelling

docs/changelog.txt

@@ -67,6 +67,7 @@ Template for new versions:
 ## API
 
 ## Lua
+- added ``GRAY`` color aliases for ``GREY`` colors
 
 ## Removed
 

docs/dev/Lua API.rst

@@ -3081,6 +3081,9 @@ environment by the mandatory init file dfhack.lua:
     COLOR_LIGHTBLUE, COLOR_LIGHTGREEN, COLOR_LIGHTCYAN, COLOR_LIGHTRED,
     COLOR_LIGHTMAGENTA, COLOR_YELLOW, COLOR_WHITE
 
+  ``COLOR_GREY`` and ``COLOR_DARKGREY`` can also be spelled ``COLOR_GRAY`` and
+  ``COLOR_DARKGRAY``.
+
 * State change event codes, used by ``dfhack.onStateChange``
 
   Available only in the `core context <lua-core-context>`, as is the event itself:

library/lua/dfhack.lua

@@ -38,6 +38,9 @@ COLOR_LIGHTMAGENTA = 13
 COLOR_YELLOW = 14
 COLOR_WHITE = 15
 
+COLOR_GRAY = COLOR_GREY
+COLOR_DARKGRAY = COLOR_DARKGREY
+
 -- Events
 
 if dfhack.is_core_context then