Test extended curses colors. Make your terminal kind of big for this one. Like 35 lines, 105 columns.

test_extended_colors.py

#!/usr/bin/env python3

# Test program for ncurses extended color pairs. (by Sam Foster, may 2024)
#
# Generates 256 foreground colors, background color 0, to use the first 256 color pairs.
# Then does the same for BG color 1, then 2, etc. until we have 256 * 256 pairs.
#
# If it works, we should end up with every combination of FG colors 0-255 and BG colors 0-255.
# If it doesn't work right, the color pairs repeat themselves.
#
# Use left and right arrows (or "j" and "k") to scroll through the color pairs. Space advances by 25 pairs.
# "q" quits.

import curses

def init_color_pairs(stdscr):
    curses.use_default_colors()
    fg_colors = 256
    bg_colors = 256
    pair = 0

    for bg in range(0, bg_colors):
        for fg in range(0, fg_colors):
            curses.init_pair(pair, fg, bg)
            pair += 1
            stdscr.addstr(1, 1, f"Initializing pair: {pair}")
            stdscr.refresh()
    return pair # total number of color pairs

def main(stdscr):
    stdscr.clear()

    pairs_to_show = 400     # how many pairs to show on screen at a given time

    total_color_pairs = 0
    hicolor_support = curses.has_extended_color_support()
    if hicolor_support:
        total_color_pairs = init_color_pairs(stdscr)

    help_string = 'j/k or left/right to scroll. space to scroll 25 pairs. < and > for home and end. q to quit'
    help_line = 26

    running = True

    c = None    # for getch()
    pair = 0    # first color pair to display on screen

    while running:

        # update screen
        status_string = f"Extended colors: {hicolor_support}, max colors: {curses.COLORS}, total pairs: {total_color_pairs}, first shown pair: {pair}"
        stdscr.clear()
        stdscr.addstr(0, 0, status_string)
        stdscr.addstr(help_line, 0, help_string)

        # draw some colors, up to 500 at a time
        line = 1
        col = 0
        for shown_pair in range(pair, min(pair+pairs_to_show, total_color_pairs)):
            try:
                stdscr.addstr(line, col, f"{shown_pair}", curses.color_pair(shown_pair))
            except:
                print(f"Error, line: {line}, col: {col}, pair: {shown_pair}")
            if col < 80:
                col += 5
            else:
                col = 0
                line += 1 
        stdscr.refresh()

        # get input
        c = stdscr.getch()
        if c == ord("q"):
            running = False

        if c == ord("k") or c == 261:   # 261 = right arrow key
            if pair < total_color_pairs - 200:
                pair += 1

        if c == ord("j") or c == 260: # 260 = left arrow key
            if pair > 0:
                pair = pair - 1

        if c == ord(" "):   # Space = go forward 25 pairs
            pair = min(pair + 25, total_color_pairs)

        if c == ord("<"):   # < = go to first page
            pair = 0

        if c == ord(">"):   # > = go to last page
            pair = max(total_color_pairs - pairs_to_show, 0)

curses.wrapper(main)