convert png to tiff doesn't work properly

[kirafishy]

hello everyone,
i want to convert a png file to tiff file, there's some transparent elements in png file, when it converted to tiff file, the colors become grey, I think the problem is tiff file doesn't have alpha channel, I tried convert option -alpha and -channel but failed, how can I convert it properly?
the link below is my example files, include the png file, tiff file and my screenshot shows the difference, thanks!
https://drive.google.com/open?id=12Z_3y ... C8nSJOUFor

[kirafishy]

wow, when i add option "-define tiff:alpha=unspecified" it works properly!