Gmapping map has mixed colors

As shown in the following picture, the resulting map produced by gmapping has mixed color dots. I have only seen gmapping producing maps with black dots for occupied grid, but not with these many colors. Is this normal behavior? If not, what might be wrong?

I am playing a rosbag file, which publishes laser scans, odometry, tf transforms and time (to /clock since I am using use_sim_time). I have much more (2 times) odometry messages than laser scan messages.

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Are you sure the colored dots are not the measurements in the LaserScan messages? Try checking the LaserScan checkbox off. Maybe it's set to visualize past measurements as well (see "decay time" field).