Transparency is controlled by the alpha channel (AA in #AARRGGBB). Maximal value (255 dec, FF hex) means fully opaque. Minimum value (0 dec, 00 hex) means fully transparent. Values in between are semi-transparent, i.e. the color is mixed with the background color.
To get a fully transparent color set the alpha to zero. RR, GG and BB are irrelevant in this case because no color will be visible. This means #00FFFFFF (“transparent White”) is the same color as #00F0F8FF (“transparent AliceBlue”). To keep it simple one chooses black (#00000000) or white (#00FFFFFF) if the color does not matter.
In the table you linked to you’ll find Transparent defined as #00FFFFFF.