Amber has a specific meaning different than red, so you probably do not want it. It indicates that you're going to turn, but with just one blinking light it will be confusing. I don't think you'll find any on the market since they would be illegal in many places, and light manufacturers aren't going to make something in a way that would limit their market.

As for what is "good" - depends a bit on your usage.

If you're going to be using it at night and in relatively light traffic, any of the 20 to 60 lumen lights are "good". The Performance Axiom Pulse 60 is very good at about $30. You really don't get into "good" tail lights until you're into the $20-$30 range anyway.

For me, I'm looking for "visible in full sunlight" - for that you need a pretty brutal light, like the Dinotte Quad Red or the DesignShine, but those are $200 taillights. I have a DesignShine.

You may also want a more brutal light if you're in brutal surroundings, like a very busy street with a lot of lighting. It takes a lot of light to get noticed when there are already 1000 flashing lights on the street.

I don't think you'll find any rear lights using AA cells. Rechargable LiIon is most common in good lights these days, a few might use AAA cells.