Fix colourized output to file

This change should be backwards compatible, but it would be better
to make the console colour API take an argument in the long term.

Fixes #1502

docs/deprecations.md

@@ -83,6 +83,11 @@ be changed so that hidden tests are included in a run only if they
 positively match a testspec.
 
 
+### Console Colour API
+
+The API for Catch2's console colour will be changed to take an extra
+argument, the stream to which the colour code should be applied.
+
 ---
 
 [Home](Readme.md#top)

include/internal/catch_console_colour.cpp

@@ -160,7 +160,8 @@ namespace {
 
     private:
         void setColour( const char* _escapeCode ) {
-            Catch::cout() << '\033' << _escapeCode;
+            getCurrentContext().getConfig().stream()
+                << '\033' << _escapeCode;
         }
     };