Alpha and indexed color transparent

Index | Transparent I can't see White in the preview on a transparent background. As soon as I convert to a transparent color, all the white becomes transparent. If I set it opaque, the object that is the same as the background color becomes white. "--M
I think it might be more interesting to follow me along with the experiment to answer this question. Downloading this experimental graphic will save you a lot of work.
If you don't download the file, start with a new file that opens a canvas for white. The left half is covered with a black rectangle. Draw a red square sized to canvas two-thirds and place it in the middle of a black and white canvas. Finally, draw a small white rectangle. Copy it and change the color to black. Move them so that the white squares are in the black part of the background and the black squares are positioned on the white background.

Select a file > Export Preview (Export Preview). Transparent type out of the lower left corner Select index color Transparency (index transparency). The white canvas and the rectangle will all become transparent. [Note: It's important to not use the eyedropper tool to pick colors.] ] All white will be restored if the option is changed to opaque (no transparency).

Finally, select Alpha Transparent (alpha transparency). The white on the canvas disappears, while the white squares are preserved. Click Cancel to exit Preview (export Preview).

Select Modify Canvas colors (Modify Canvas color). Change the white background to black and change the black to white. Also, swap the colors inside the red box.

As you have just done, go to the export Preview (exporting Preview) and select index-color transparency (index transparency). The black of the background will disappear. Then select opacity (no transparency).

This time when you select alpha-transparent (alpha transparency), the inner black square remains unchanged.

Index color is the color of the canvas, which is the back color. Alpha values range from 0 (black) to 255 (white), black for transparent, and white for opaque. If the white part of your picture is attached to a color, then even if the background is white, the white part of your image is still opaque after using alpha transparency (alpha transparency).
Since Black is basically a representation of transparency based on the alpha color spectrum, why is the black rectangle in the middle of the picture in the last instance still preserved? I guess it's because the program doesn't know why it can't see it through its attached color. Perhaps the expert here can give us an authoritative answer, then I will be very happy to publish here.
At the same time I would like to say, Macromedia, or do not make changes!