I had 2 pristella tetras I bought at a pet shop. I had them in my 10g tank until it leaked (my old one) and put them in my 20. Then a few weeks later I got 4 more at petco and put them in the 10g tank (new one) with the intention of moving the 2 back into it. My plans changed and tonight I put the 4 that were in the 10g into the 20 with the other 2. I noticed that there's a huge difference between them. The first two are more of a yellowish tone and the other 4 are more of a silverish. I'll try to take pics tomorrow. I knew they seemed different but thought it was the different lighting between the two tanks (two different rooms, etc). Any thoughts? It doesn't appear to matter to them-all six started schooling right away.