I did the same thing as you a few years ago and it became very easy for me to see afterimages (auras of colour). It is interesting to note, though, that I didn't see any astral auras until I was well into NEW development. Even then, I've only actually seen one astral aura to date. I saw it around another person about ten feet away while I was using the etheric wrap technique on my left thumb (to heal a blood blister). For what it's worth, I'd suggest trying NEW while practicing aura viewing exercises. It is very easy to do both at the same time, as neither one really requires that much concentration.
Malcolm
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