diff --git a/TileGenerator.cpp b/TileGenerator.cpp
index c093010..a131dc8 100644
--- a/TileGenerator.cpp
+++ b/TileGenerator.cpp
@@ -140,6 +140,7 @@ TileGenerator::TileGenerator():
 	m_geomX2(2048),
 	m_geomY2(2048),
 	m_exhaustiveSearch(EXH_AUTO),
+	m_renderedAny(false),
 	m_zoom(1),
 	m_scales(SCALE_LEFT | SCALE_TOP),
 	m_progressMax(0),
@@ -542,6 +543,7 @@ void TileGenerator::renderMap()
 		}
 		if (!m_readPixels.full())
 			renderMapBlockBottom(blockStack.begin()->first);
+		m_renderedAny |= m_readInfo.any();
 	};
 	auto postRenderRow = [&] (int16_t zPos) {
 		if (m_shading)
@@ -847,6 +849,11 @@ void TileGenerator::printUnknown()
 	std::cerr << "Unknown nodes:" << std::endl;
 	for (const auto &node : m_unknownNodes)
 		std::cerr << "\t" << node << std::endl;
+	if (!m_renderedAny) {
+		std::cerr << "The map was read successfully and not empty, but none of the "
+			"encountered nodes had a color associated.\nCheck that you're using "
+			"the right colors.txt. It should match the game you have installed." << std::endl;
+	}
 }
 
 void TileGenerator::reportProgress(size_t count)
diff --git a/include/TileGenerator.h b/include/TileGenerator.h
index f2e81db..0f1c8f7 100644
--- a/include/TileGenerator.h
+++ b/include/TileGenerator.h
@@ -43,17 +43,19 @@ struct BitmapThing { // 16x16 bitmap
 		for (int i = 0; i < 16; ++i)
 			val[i] = 0;
 	}
-	inline bool full() const {
+	inline bool any_neq(uint16_t v) const {
 		for (int i = 0; i < 16; ++i) {
-			if (val[i] != 0xffff)
-				return false;
+			if (val[i] != v)
+				return true;
 		}
-		return true;
+		return false;
 	}
+	inline bool any() const { return any_neq(0); }
+	inline bool full() const { return !any_neq(0xffff); }
 	inline void set(unsigned int x, unsigned int z) {
 		val[z] |= (1 << x);
 	}
-	inline bool get(unsigned int x, unsigned int z) {
+	inline bool get(unsigned int x, unsigned int z) const {
 		return !!(val[z] & (1 << x));
 	}
 
@@ -148,11 +150,12 @@ private:
 	int m_mapWidth;
 	int m_mapHeight;
 	int m_exhaustiveSearch;
+	std::set<std::string> m_unknownNodes;
+	bool m_renderedAny;
 	std::map<int16_t, std::set<int16_t>> m_positions; /* indexed by Z, contains X coords */
 	ColorMap m_colorMap;
 	BitmapThing m_readPixels;
 	BitmapThing m_readInfo;
-	std::set<std::string> m_unknownNodes;
 	Color m_color[16][16];
 	uint8_t m_thickness[16][16];