Description

When create PNG file with transparent background, Microsoft Internet Explorer (at least version less or equal 6) draws it incorrectly. It blends all the transparent and semi-transparent areas with the gray color. Other browsers display the same image without any problems.
Reason

It is a bug of Microsoft Internet Explorer.

Solution

As it is bug of Microsoft, you should wait fix of this problem in Internet Explorer and don't use transparent PNG files. Note, the problem occurs only if color depth of PNG is 32. For 8 bpp PNG (and GIF) files transparency is supported without problems. Unfortunately 8 bpp images don't provide full-value alpha channel, however sometimes it is sufficient solution, which even has its own advantages (less size).

Besides of it, you can use such a PNG files if the background of the page which contains the image is gray too.

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Best regards,
Fedor Skvortsov