diff --git a/src/common/Color.cpp b/src/common/Color.cpp
index 54629397..433391f3 100644
--- a/src/common/Color.cpp
+++ b/src/common/Color.cpp
@@ -416,7 +416,7 @@ void Color::upgrade ()
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-std::string Color::colorize (const std::string& input)
+std::string Color::colorize (const std::string& input) const
 {
   std::string result;
   _colorize (result, input);
@@ -435,7 +435,7 @@ std::string Color::colorize (const std::string& input)
 //
 //   256 fg               \033[38;5;Nm
 //   256 bg               \033[48;5;Nm
-void Color::_colorize (std::string &result, const std::string& input)
+void Color::_colorize (std::string &result, const std::string& input) const
 {
   if (!nontrivial ())
   {
diff --git a/src/common/Color.h b/src/common/Color.h
index e8db5100..2185ea4b 100644
--- a/src/common/Color.h
+++ b/src/common/Color.h
@@ -58,9 +58,9 @@ public:
   void upgrade ();
   void blend (const Color&);
 
-  std::string colorize (const std::string&);
+  std::string colorize (const std::string&) const;
   static std::string colorize (const std::string&, const std::string&);
-  void _colorize (std::string&, const std::string&);
+  void _colorize (std::string&, const std::string&) const;
   static std::string strip (const std::string&);
 
   bool nontrivial () const;