In deviation from the instructions for icons, we now recommend the free Greenfish Icon Editor Pro.
In the picture you can see the settings for a transparent background.
When it comes to colors, you should always try to use the standard screen colors. You can find these by clicking on the three dots at the bottom right. The color must be selected in the left window next to the transparent window for the background (checkerboard pattern).
Save the result e.g. B. as a bmp file for insertion into the IMC icon library.