The color you see of the trasparency doesn't really matter since it's not going be seen once it's uploaded to a web site... Those are just colors you see with certain image viewers. ACDSee shows transparency as "black".
GIF or GIF with transparency files must be created using index colors, 256 or less. They cannot maintain transparency with greyscale, RGB, CMYK, Lab Colors, etc. You'll find that using JPG with the same color background is a better choice under certain circumstances where more than 256 colors is required to view the image optimally...