==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

minetest.register_chatcommand("dumpnodes", {
	params = "",
	description = "",
	func = function(plname, param)
		local n = 0
		local ntbl = {}
		for nn, nd in pairs(minetest.registered_nodes) do
			local prefix, name = nn:match('(.*):(.*)')
			if prefix == nil or name == nil or prefix == '' or name == '' then
				-- nothing
			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 minetest.chat_send_player(plname, 'io.open: ' .. err)
		end
		for prefix, i in pairs(ntbl) do
			out:write('# ' .. prefix .. '\n')
			for name, nd in pairs(i) do
				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
				end
			end
			out:write('\n')
		end
		out:close()
		minetest.chat_send_player(plname, n .. " nodes dumped.")
	end,
})
==FILE== avgcolor.py
#!/usr/bin/env python
import sys
from PIL import Image

def avg2(a, b):
	return int((a + b) / 2.0)

def avg2t3i0(a, b):
	return tuple(avg2(t[0], t[1]) for t in zip(a[:3], b[:3]))

if len(sys.argv) <= 1:
	print("Usage: %s <input>" % sys.argv[0])
else:
	inp = Image.open(sys.argv[1])
	inp = inp.convert('RGBA')
	ind = inp.load()
	avgc = -1
	for x in range(inp.size[0]):
		for y in range(inp.size[1]):
			pxl = ind[x, y]
			if pxl[3] < 128:
				continue
			if avgc == -1:
				avgc = pxl[:3]
			else:
				avgc = avg2t3i0(avgc, pxl)
	if avgc == -1:
		sys.stderr.write('Warning: did not find average color\n')
		print('0 0 0')
	else:
		print("%d %d %d" % avgc)

==COMMAND==
while read -r p; do
	set -- junk $p
	shift
	if [[ ! $1 == "#" && ! $1 == "" ]]; then
		echo $1 `python /path/to/avgcolor.py $(find /minetest/dir -type f -name $2)`
	fi
done < nodes.txt > colors.txt
# Use nicer colors for water and lava
sed -re 's/^default:water_([a-z]+) [0-9 ]+$/default:water_\1 39 66 106/' < colors.txt > tmp$$ && mv tmp$$ colors.txt
sed -re 's/^default:lava_([a-z]+) [0-9 ]+$/default:lava_\1 255 100 0/' < colors.txt > tmp$$ && mv tmp$$ colors.txt
==INSTRUCTIONS==
1) Get avgcolors.py running
2) Add the dumpnodes mod to Minetest
3) Create a world and load dumpnodes & all mods you want to have a color entry for
4) Execute /dumpnodes ingame
5) Use the command to generate colors.txt