I switched to Windows 7 + outlook 2010 for my working laptop several weeks before.Then I found the color category always appear on email I send out and new email I get automatically. Finally Microsoft has confirmed it is caused by design.
I used to use color category to organize my email and divided them into "to-do" and "waiting" based on different priority. Now it doesn't work. And stupid outlook "follow up" flag couldn't change color. Right now I have to remove color category by hand on some email.
Email from Microsoft: Symptom: You are currently having a problem with categories on Outlook 2010 client. Specifically since the migration from Outlook 2003, you are seeing inconsistent behavior regarding the color categories. If you add a color category to an email and then reply, the category will be shown on the reply message as well. Other users don't have this problem so far. Cause: By design Resolution: If you put a category on an email when you receive it (a new email and not a reply from a conversation) the category information will follow on all the other replies that will be sent on this thread. Even though you later remove the category, if you reply to this email or any other email from the conversation, it will still keep the original category. However if you put a category on an email after you already sent and received emails on that conversation, and you then reply to that email, the reply will not have the category. To make sure the thread doesn’t contain category information you can click on the category square from the conversation title (the upper most header of a conversation) to clear all the categories from that thread. This is why you couldn’t reproduce the problem with a new email. I have confirmed this along several tests and even with an Escalation Engineer. It is considered by design because the information is stored on the entire conversation, but there are ways to avoid it if you place the category on the emails after sending at least one reply. Thank you for your collaboration, Best regards,