There are several possible scenarios:
1. If you see some brown particles evenly mixed with the largely blue particles, it is normal. There are two kinds of materials inside the cartridge. Their initial colors are blue and brown respectively.
2. If there is a thin layer of brown material at the top or bottom of the anti-calc cartridge, it is normal. It is possible for some of the material in the anti-calc cartridge (especially the top layer) to change color before use due to exposure to atmospheric conditions. This does not affect the effectiveness of the cartridge.
3. If the anti-calc cartridge is completely brown when you open the packaging, it is not fit for use.