problem with the data format of velodyne lidar

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hi guys! Recently,I had run the velodyne lidar .when i used rviz to visualise the data stream received from the lidar ,i saw different color in different point.well,this is where my problem is:does velodyne itself produce data with color information or it is rviz that attaches the information to the velodyne raw data ? if it is the rviz,then what principle does it follow when it created the color to certain point,that is ,what does the color of point stand for?this is my first question .then i transformed the velodyne raw data into the pcl::PointCloud(pcl::PointXYZRGB) format,and broadcasted them into the same format after some processing with my program,but this time,the program warned that it can't find the rgb field .does it mean that velodyne raw data at nature doesn't own the rgb channels,so when i transform them into rgb format,some error just occured? i can't find any useful information on internet and hope for some help here,thanks a lot!