diff --git a/include/wx/motif/colour.h b/include/wx/motif/colour.h
index a255c64558..531d86085f 100644
--- a/include/wx/motif/colour.h
+++ b/include/wx/motif/colour.h
@@ -27,7 +27,7 @@ public:
     // default
   wxColour();
     // from RGB
-  wxColour( char red, char green, char blue );
+  wxColour( unsigned char red, unsigned char green, unsigned char blue );
     // implicit conversion from the colour name
   wxColour( const wxString &colourName ) { InitFromName(colourName); }
   wxColour( const char *colourName ) { InitFromName(colourName); }
diff --git a/include/wx/msw/colour.h b/include/wx/msw/colour.h
index fabd5ad99c..4770bf7a53 100644
--- a/include/wx/msw/colour.h
+++ b/include/wx/msw/colour.h
@@ -24,7 +24,7 @@ public:
     // default
   wxColour();
     // from RGB
-  wxColour( char red, char green, char blue );
+  wxColour( unsigned char red, unsigned char green, unsigned char blue );
     // implicit conversion from the colour name
   wxColour( const wxString &colourName ) { InitFromName(colourName); }
   wxColour( const char *colourName ) { InitFromName(colourName); }
diff --git a/include/wx/stubs/colour.h b/include/wx/stubs/colour.h
index 0f592f5789..8304b2d917 100644
--- a/include/wx/stubs/colour.h
+++ b/include/wx/stubs/colour.h
@@ -27,7 +27,7 @@ public:
     // default
   wxColour();
     // from RGB
-  wxColour( char red, char green, char blue );
+  wxColour( unsigned char red, unsigned char green, unsigned char blue );
     // implicit conversion from the colour name
   wxColour( const wxString &colourName ) { InitFromName(colourName); }
   wxColour( const char *colourName ) { InitFromName(colourName); }