diff --git a/libs/gfx/include/psemek/gfx/color.hpp b/libs/gfx/include/psemek/gfx/color.hpp
index 98998c87..74c5b37a 100644
--- a/libs/gfx/include/psemek/gfx/color.hpp
+++ b/libs/gfx/include/psemek/gfx/color.hpp
@@ -105,7 +105,8 @@ namespace psemek::gfx
 	template <std::size_t N>
 	geom::vector<float, N> light(geom::vector<float, N> c, float lightness = 0.5f)
 	{
-		for (std::size_t i = 0; i < N; ++i)
+		static_assert(N == 3 || N == 4);
+		for (std::size_t i = 0; i < 3; ++i)
 			c[i] = geom::lerp(c[i], 1.f, lightness);
 		return c;
 	}
@@ -113,7 +114,8 @@ namespace psemek::gfx
 	template <std::size_t N>
 	geom::vector<float, N> dark(geom::vector<float, N> c, float darkness = 0.5f)
 	{
-		for (std::size_t i = 0; i < N; ++i)
+		static_assert(N == 3 || N == 4);
+		for (std::size_t i = 0; i < 3; ++i)
 			c[i] = geom::lerp(c[i], 0.f, darkness);
 		return c;
 	}