I was wondering if the font color of the life tile has to be white in all cases.
Basically I like to update my tile title at a specific time using TileUpdateManager and TileNotification to show the user some information (like an alarm time)
I have downloaded so many apps now and all tile titles are in white.
I am not sure If I am on the right track wanting to update the app tile title using another font color.
As you can see on http://msdn.microsoft.com/en-US/library/windowsphone/design/jj662929(v=vs.105).aspx , there is no possibility of changing the default text color in the Live Tiles - the font color is white, because is the only color that matches on all the accents color.
The reason of this choice is quite clear. You just have to imagine a phone with dark blue accent color on the tiles and black text: this would make the tile content unreadable.
By the way, using the font color to notify the user on something is the worst way to do it, when you have a whole Live Tile to use. You may choose to display a different image, write different text, and so on; this changes would be much more effective for the user than a mere font color change.
My suggestion is to read this article on MSDN: http://msdn.microsoft.com/en-us/library/windowsphone/design/jj662929(v=vs.105).aspx . Here you can find many relevant suggestions on how to design your Live Tile and how to be effective in displaying information to the user.
I also suggest you not to use Tiles for important notifications, like alarms, as MSDN documentation states:
"Don't rely on Tiles to send urgent, real-time info to the user. For instance, a Tile is not the right surface for a communication app to inform the user of an incoming call. Toast notifications are a better medium for real-time messages."