message: Add comments for event color_index
diff: @@ -137,7 +137,11 @@ struct trace_event_t
  uint32_t graph_row_id;
  uint32_t color; // color of the event (or 0 for default)
  - uint32_t color_index; // -1 or colors_t enum value like col_Graph_Bari915SubmitDelay
  +
  + // i915 events: col_Graph_Bari915SubmitDelay, etc
  + // ftrace print events: buf hashval for colors
  + // otherwise: -1
  + uint32_t color_index;
  int64_t ts; // timestamp
  int64_t duration; // how long this timeline event took (or INT64_MAX for not set)
  