I downloaded these DEM files, http://www.dgadv.com/srtm30/
srtm30 globe. I open the DEM files in Multispec. Some of them are black and white, some are automatically grayscale. 

How do I get them all in grayscale? 

(attaching image to explain) 


![enter image description here][1]


![enter image description here][2]


  [1]: https://i.sstatic.net/a2rUd.jpg
  [2]: https://i.sstatic.net/FZYdc.jpg