As described in ClickOnce installing dialog icon (StackOverflow) icons displayed in the ClickOnce installing dialog may seem noisy:
It should be looking like this
This is because the ClicOnce API does not seem to support alpha with the .ico file format. In fact, most legacy APIs don't support alpha well. Instead it seems to use the color value of the pixel in the lower left corner of the image.
The workaround is then to just add transparent extra column as described below.
Step1: Add transparent pixel in lower left corner using Paint.Net
- Open .ico file in Paint.net (all layers/images)
- Image resize 256x256 -> 255x255
- Canvas resize 255x255 -> 256x256 (place image image bottom/right)
- Save as new .ico-file
Step 2: Optimize Icon using IcoFx
Paint.net does seem to save .ico files always using 24 or 32 bit including alpha. For simple icons you may optimize all images to a simpler data type. You can do this in IcoFx by selecting an image and then using Image -> Data Type.
Most of the time i get along using optimized 256 colors (8 bit). I definitely recommend removing alpha unless you have good reason to keep it.