Hello,
Thank you for contacting Farouk Systems.
Reason for the brown spots are the Silk proteins settling in the bottles. The Silk is suspended in the formula with the help of a small amount of alcohol. If the bottle is not sealed tightly, the alcohol could evaporate, allowing the precipitation of the silk proteins. Normally, we advise shaking the bottles vigorously before use to disperse the silk.
If you have questions or need further help, please feel free to email me or contact our customer service department Monday through Friday 8am- 5pm central time 1-800-237-9175.