Change Application Bar icon color in light theme - Windows Phone 7

I have a favourite icon on the ApplicationBar that I want to change to yellow image when the item is favourited. This works well on Dark Theme but when the user change to White Theme, it becomes black all the time. Actually, the color changes to yellow for around 1 second and then change to black.

I am testing on Windows Phone 7 Emulator, not test with de开发者_如何学Govice yet

The best answer I have found for this so far is from the UI Design and Integration Guide for Windows Phone 7 v2.0. It says colored icons cause the Application Bar to display unpredictably.

Extract below:

"Application Bar Icon images should be 48 pixels by 48 pixels and have a white foreground on a transparent background using an alpha channel. The Application Bar will colorize the icon according to the current style settings and colored icons can cause this effect to display unpredictably."