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Can you please share which version of Kendo UI Mobile have you previously used? I have tested with several versions back and all of them have the described "darkening" on transition. This is the default native ios7 behavior and the effect has been intended by design.
If you want to change this darkening or its color, you will have to override the ios7 theme CSS styles. You can see the base styles for the ios7 theme here
. You need the ones at the bottom that are labeled as /* transitions */. As you can see the brightness is lowered to 70%. You can override these styles and play with them.
I hope this information is helpful. Let me know if you have any other questions.