The white is just he background color. It looks like the middle part was featureless for the most part so it doesn't have that many dots. Your overlap looks like it was fine.
The elevation information is in the DEM file in the Advanced Outputs section. You can see the elevation layer in the map by choosing the 'Elev' option in the top right layer controls. You can also mouse over any spot in the map and see that value in the top right.