How to keep transparent colour when saving PNG

[Immortalninja]

Hi,
I recently got a new computer and updated IrfanView to 4.2 and am seeing some differences (the old one was reallllly old). I've had a searce but havent been able to find exactly the answer I'm looking for.
Anyway, I have a bitmap image that I want to save to png. The transparent colour is bright pink. When I save as a png it asks me to click on which pixel colour I want to be transparent.
This all works fine, apart from one thing. The saved image will have the transparent colour changed to black.
Is there anyway to preserve the pink as the transparent colour?

Thanks for your time and help

KK

[Bhikkhu Pesala]

If you click on pink, then the transparent colour is pink. What you see in IrfanView when viewing transparent images is the default window colour (properties, viewing), which is black but can be changed to any other colour.

[Immortalninja]

I dont think thats the issue I am having.
It actually changes the palette entry to black.
I've attached the two images.
Pre.png is the image saved to png with the pink back ground that should be trasparent.
When I save and click on the pink areas during save I get post.png. While the transparency is correctly set the transparent colour has been changed to black in the palette.

Does anyone know why this is and how to stop it?

Thanks

KK

[j7n]

I tested this issue and the palette entry 0 remained rgb(255,0,255) after setting it transparent using IrfanView. It is still pink in post.png too.