==FILE== mods/dumpnodes/init.lua
local function nd_get_tiles(nd)
	if nd.tiles then
		return nd.tiles
	elseif nd.tile_images then
		return nd.tile_images
	end
	return nil
end

local function pairs_s(dict)
	local keys = {}
	for k in pairs(dict) do
		table.insert(keys, k)
	end
	table.sort(keys)
	return ipairs(keys)
end

minetest.register_chatcommand("dumpnodes", {
	params = "",
	description = "",
	func = function(plname, param)
		local n = 0
		local ntbl = {}
		for _, nn in pairs_s(minetest.registered_nodes) do
			local nd = minetest.registered_nodes[nn]
			local prefix, name = nn:match('(.*):(.*)')
			if prefix == nil or name == nil or prefix == '' or name == '' then
				print("ignored(1): " .. nn)
			else
				if ntbl[prefix] == nil then
					ntbl[prefix] = {}
				end
				ntbl[prefix][name] = nd
			end
		end
		local out, err = io.open('nodes.txt', 'wb')
		if not out then
			return true, "io.open(): " .. err
		end
		for _, prefix in pairs_s(ntbl) do
			local nodes = ntbl[prefix]
			out:write('# ' .. prefix .. '\n')
			for _, name in pairs_s(nodes) do
				local nd = nodes[name]
				if nd.drawtype ~= 'airlike' and nd_get_tiles(nd) ~= nil then
					local tl = nd_get_tiles(nd)[1]
					if type(tl) == 'table' then
						tl = tl.name
					end
					tl = (tl .. '^'):match('(.-)^')
					out:write(prefix .. ':' .. name .. ' ' .. tl .. '\n')
					n = n + 1
				else
					print("ignored(2): " .. prefix .. ':' .. name)
				end
			end
			out:write('\n')
		end
		out:close()
		return true, n .. " nodes dumped."
	end,
})
==FILE== avgcolor.py
#!/usr/bin/env python
import sys
from PIL import Image

def tsum(a, b):
	return tuple(sum(e) for e in zip(a, b))

if len(sys.argv) < 2:
	print("Prints average color (RGB) of input image")
	print("Usage: %s <input>" % sys.argv[0])
	exit(1)

inp = Image.open(sys.argv[1])
inp = inp.convert('RGBA')
ind = inp.load()

cl = (0, 0, 0)
counted = 0
for x in range(inp.size[0]):
	for y in range(inp.size[1]):
		px = ind[x, y]
		if px[3] < 128:
			continue
		cl = tsum(cl, px[:3])
		counted = counted + 1

if counted == 0:
	sys.stderr.write("didn't find avg. color for %s\n" % sys.argv[1])
	print("0 0 0")
	exit(0)

cl = tuple(int(n / counted) for n in cl)
print("%d %d %d" % cl)
==SCRIPT==
#!/bin/bash -e

AVGCOLOR_PATH=/path/to/avgcolor.py
MTGAME_PATH=/path/to/minetest_game
NODESTXT_PATH=./nodes.txt
COLORSTXT_PATH=./colors.txt

while read -r line; do
	set -- junk $line
	shift
	if [[ -z "$1" || $1 == "#" ]]; then
		echo $line
		continue
	fi
	tex=$(find $MTGAME_PATH -type f -name "$2")
	if [ -z "$tex" ]; then
		echo "skip $1: texture not found" >&2
		continue
	fi
	echo $1 $(python $AVGCOLOR_PATH "$tex")
	echo "ok $1" >&2
done < $NODESTXT_PATH > $COLORSTXT_PATH
# Use nicer colors for water and lava:
sed -re 's/^default:((river_)?water_(flowing|source)) [0-9 ]+$/default:\1 39 66 106 128 224/g' $COLORSTXT_PATH -i
sed -re 's/^default:(lava_(flowing|source)) [0-9 ]+$/default:\1 255 100 0/g' $COLORSTXT_PATH -i
# Add transparency to glass nodes:
sed -re 's/^default:(.*glass) ([0-9 ]+)$/default:\1 \2 64 16/g' $COLORSTXT_PATH -i
sed -re 's/^doors:(.*glass[^ ]*) ([0-9 ]+)$/doors:\1 \2 64 16/g' $COLORSTXT_PATH -i
# Fix xpanes color:
sed -re 's/^xpanes:((pane|bar)(_flat)?) [0-9 ]+$/xpanes:\1 194 194 227 64 16/g' $COLORSTXT_PATH -i
==INSTRUCTIONS==
1) Make sure avgcolors.py outputs the usage instructions
2) Add the dumpnodes mod to Minetest
3) Create a world and load dumpnodes & all mods you want to generate colors for
4) Execute /dumpnodes ingame
5) Run the script to generate colors.txt (make sure to replace /path/to/... with the actual paths)