+ SVr3.2 introduced color support to curses in 1987.
+
+ SVr4 made internal changes, e.g., moving the storage for the color
+ state from SP (the SCREEN structure) to cur_term (the TERMINAL struc-
+ ture), but provided the same set of library functions.
+
+ SVr4 curses limits the number of color pairs to 64, reserving color
+ pair zero (0) as the terminal's initial uncolored state. This limit
+ arises because the color pair information is a bitfield in the chtype
+ data type (denoted by A_COLOR).
+
+ Other implementations of curses had different limits:
+
+ o PCCurses (1987-1990) provided for only eight (8) colors.
+
+ o PDCurses (1992-present) inherited the 8-color limitation from PC-
+ Curses, but changed this to 256 in version 2.5 (2001), along with
+ changing chtype from 16-bits to 32-bits.
+
+ o X/Open Curses (1992-present) added a new structure cchar_t to store
+ the character, attributes and color-pair values, allowing increased
+ range of color-pairs. Both color-pairs and color-values used a
+ signed short, limiting values to 15 bits.
+
+ o ncurses (1992-present) uses eight bits for A_COLOR in chtype val-
+ ues.
+
+ Version 5.3 provided a wide-character interface (2002), but left
+ color-pairs as part of the attributes-field.
+
+ Since version 6 (2015), ncurses uses a separate int for color-pairs
+ in the cchar_t values. When those color-pair values fit in 8 bits,
+ ncurses allows color-pairs to be manipulated via the functions us-
+ ing chtype values.
+
+ o NetBSD curses used 6 bits from 2000 (when colors were first sup-
+ ported) until 2004. At that point, NetBSD changed to use 10 bits.
+ As of 2021, that size is unchanged. Like ncurses before version 6,
+ the NetBSD color-pair information is stored in the attributes field
+ of cchar_t, limiting the number of color-pairs by the size of the
+ bitfield.
+
+