I have read the Fowler books and Ed Caffrey's web site regarding etching blades to reveal grain and differential treating. I recently etched a 1084 blade and the dark etched blade showed me the spine and edge differences. After resanding the blade back to 600 grit all dark etch color and quench line are gone and I don't see a grain. Is this because of my steel choice or am I missing something?

To see an etching line you often have to take a blade past 800 grit to see the hardening line.  On some blades you need to get the blade to the finish you want and then give it a short etch to bring out the hamon.  How well a hamon shows depends on the hardening process, and heat treatment you gave the blade.  Simple steel when treated properly show a very nice hamon.  

If you hardened in oil it can be tough to get a good hamon.