fix missing header

Author: nathanhhughes

include/spark_dsg/color.h

@@ -148,4 +148,4 @@ struct Color {
   static const std::vector<Color> ironbow_colors_;
 };
 
-}  // namespace spark_dsg
+}  // namespace spark_dsg

src/color.cpp

@@ -1,6 +1,7 @@
 #include "spark_dsg/color.h"
 
 #include <algorithm>
+#include <array>
 #include <random>
 
 namespace spark_dsg {