Let me clear this up for everyone once and for all.
White -> Connected to wifi, but not Google's servers.
Blue/Green/Any Color -> In sync with Google's servers.
Your connection will go 'white' for any number of reasons. One of them is as someone already mentioned, default wifi is set to sleep after a period of inactivity. This basically powers down the wifi radio to a minimal state, and the connection to Google's servers is lost. Without the connection to Google's servers, all sync is gone. All of it. Email, facebook, you name it. You can change this using advanced wifi settings and setting it to never sleep.
Sometimes, when you wake your device it won't sync to Google's servers right away. A simple fix for this is to open the Talk application, as it is what Google uses for user authentication for the whole device. Even the market won't work if you're not authenticated through Google Talk.
Let me know if any of you have any other questions.