This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Particle Color outputs zero when being used with World Position Offset in the material editor.
The material displays no world position offset
The material is offset by the value multiplied by particle color
Head over to the existingAnswerHub thread and let us know what's up.