Custom POI icons on map

Hi POI Factory,

Here's a simple question for you. I am sure you all know this, but for some reasons the answer eludes me.

When using POI Loader to create a .gpi file, you can specify an icon file with the same name as your .csv or .gpx file and this icon will be shown on the map at each POI locations.

Questions:

Those icons are straight RGB bitmaps, most probably 24-bit bitmaps, right? 24-bit bitmaps have only R, G, B colors.

How come some of these logos have transparency?

For example, I have a food logo (like the Food Network logo) which is a red circle filled in red with the white word "food" in the middle. Stangely, the outside of the circle seems white to me, but ends up as transparent on the map so it is like the logo is only the red circle and not a red circle with a white square box around it.

Is there a rule of color for the keying? It seems that a color (255,255,255) is white, but (253,253,253) is transparent.

Am I the only guy here that does not get this? If there are specific colors to use to have transparency, there has to be a document somewhere. How do you do this? Are you just making square logos?

Thanks for your help. I am totally puzzled.

Turbo