PS6, convert BMP to GIF, white areas problem

Hi evryone,

I'd like to convert BMP pic to Gif pic in order to erase the background into
transparent. It's for icons in my application.
The problem is that for all white colors, the white areas are displayed as
the background color.
Ex, an icon in a tollbar, my toolbar background is in buttonFace color (gray
by default), the white areas of my icon are in gray !

In IE, the white areas are well displayed in white.

When I save my pic in gif format, the image mode is set to indexed and there
are the right number of colors (+transparent one)

I know that I've succeeded to make my icon "white"

PhotoShop 6