make tests portable by using 565 compatible colors

gm/stringart.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkPath.h"
@@ skipping 37 matching lines @@
                                        length*SkScalarSin(step) + center.fY);
             path.lineTo(rp);
             length += angle / SkScalarHalf(SK_ScalarPI);
             step += angle;
         }
         path.close();
 
         SkPaint paint;
         paint.setAntiAlias(true);
         paint.setStyle(SkPaint::kStroke_Style);
-        paint.setColor(0xFF007700);
+        paint.setColor(sk_tool_utils::color_to_565(0xFF007700));
 
         canvas->drawPath(path, paint);
     }
 
 private:
     typedef GM INHERITED;
 };
 
 DEF_GM( return new StringArtGM; )