For user affter migration from Exchange 2010 to Exchange 2013, color category which set up in outlook 2010 has been disappearing.

Have you ever heard the issue?

Hi,

According to your description, I understand that color category which set up in outlook 2010 disappeared after finish migrating form Exchange 2010 to Exchange 2013.
If I misunderstand your concern, please do not hesitate to let me know.

Color category will also move to new Exchange server when migrate Exchange 2010 to Exchange 2013.

For your question, I want to double confirm whether all account or special user experience this question. Please try below method to troubleshooting your question:
1. Try to recreate new Outlook profile for testing.
2. Open Outlook and right click mailbox name and select Data File Properties then click Upgrade to Color Categories, figure as below:
 
3. Finally, we can try below steps in Restore the color categories: http://office.microsoft.com/en-us/outlook-help/restore-the-default-color-categories-HA010217889.aspx

Thanks