diff --git a/dgl/Color.hpp b/dgl/Color.hpp
index fbce9cc2..51534734 100644
--- a/dgl/Color.hpp
+++ b/dgl/Color.hpp
@@ -68,7 +68,7 @@ struct Color {
    /**
       Create a new color based on this one but with a different alpha value.
     */
-    Color withAlpha(float alpha) noexcept;
+    Color withAlpha(float alpha) const noexcept;
 
    /**
       Create a color specified by hue, saturation and lightness.
diff --git a/dgl/src/Color.cpp b/dgl/src/Color.cpp
index 10382fbd..454ada38 100644
--- a/dgl/src/Color.cpp
+++ b/dgl/src/Color.cpp
@@ -114,7 +114,7 @@ Color::Color(const Color& color1, const Color& color2, const float u) noexcept
     interpolate(color2, u);
 }
 
-Color Color::withAlpha(const float alpha2) noexcept
+Color Color::withAlpha(const float alpha2) const noexcept
 {
     Color color(*this);
     color.alpha = alpha2;