Question: Once I've baked a texture and want to save it - by default Blender offers me to save it as PNG RGBA, I change it to PNG RGB (no alpha) and save it. 

The problem is that every time I re-bake the same texture and simply hit Save, it somehow saves as PNG RGBA again, not RGB as I saved it initially.

So I have two questions:

1. Why is it not remembering my file format when saving with "Save", not with "Save as" (from uv window)?
2. Where can I set its defaults to PNG RGB, so that every time I save a baked texture I won't have to go and click PNG RGB?

Answer: 
To change the default image file type produced by Blender, you actually want to change the image settings in the Render panel.

To change the default for a single file, go to the Properties>Render panel and scroll down to the 'Output' submenu. Then select the file format and BW/RGB/RGBA to your desired format.

![enter image description here](https://i.stack.imgur.com/Lfv1B.png)

If you want to set this as your default image type for *all* of your projects, first open a new file or open a new instance of Blender. Change the settings to what you would like to be default, then press `Ctrl`+`U`.

This changes your startup .blend file so that when you open future projects, they will come preloaded with these settings. It will not affect any of your old .blend files.
It keeps defaulting to RGBA because the image has a alpha channel (and is trying not to loose information). Uncheck the Alpha option when creating the image and it'll default to RGB.

![New image dialog](https://i.stack.imgur.com/CeTOi.png)