I think one thing I forgot to mention is that I always use images as palettes. If I open all images in layer mode and index them (GIMP loads depending on how many images you have opened), I right-click the palette box and select "Rearrange Colormap." You drag that color box of the background to the first box or the very top-left corner. Hit enter and you can save one image as a png file for a palette. No need to worry about saving the rest manually. Well, that's me when it comes to saving one image as/for a palette instead of making palette files. I know there are people who do different ways of saving files for palettes and I'm fine with those who do differently, such as using Alferd Spritesheet Unpacker to split from sprite sheets to separate image.
About opening all images as layers, I always open one image first (especially the first one) before I start dragging the rest into layer mode. That way, I don't have to go with selecting an option of opening images as layers unless I feel like to.
The first time I tried that, it had original bor.exe and when I tried it, it was WAY too limited for me to code. The one I struggled most was creating new color palettes but at that time, I didn't know how to create new colors. I was stuck to relying on the old pal.act file. It took me a bit over one and a half years to get that working until I looked at one old mod of Zangief (as a protagonist). I also struggled with the old engine until I figured out by substituting bor.exe with OpenBOR.exe. It took me 3-4 months until I started to use OpenBOR.exe. About png's, there were no png's for OpenBOR at that time until the engine was updated. But I do remember the first time I used png was early 2010.
I need someone to enlighten me when png made its debut in OpenBOR because I forgot when exactly that happened.
Me neither, as I was curious about the use of 24-bit type because it was mentioned by
@DCurrent, and I have no clue about using that at all. Except it could be used for levels. But I don't bother using that. We let him or anyone here who has better knowledge of that enlighten us. I only save an image with just png and that's it.
If you want to know how to start OpenBOR, take a look at this.
A collection of useful information to get started with OpenBOR