Call this method in your app constructor
private void LightTheme()
{
((SolidColorBrush)Resources["PhoneRadioCheckBoxCheckBrush"]).Color = ((SolidColorBrush)Resources["PhoneRadioCheckBoxBorderBrush"]).Color = ((SolidColorBrush)Resources["PhoneForegroundBrush"]).Color = Color.FromArgb(0xDE, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneBackgroundBrush"]).Color = Color.FromArgb(0xFF, 0xFF, 0xFF, 0xFF);
((SolidColorBrush)Resources["PhoneContrastForegroundBrush"]).Color = Color.FromArgb(0xFF, 0xFF, 0xFF, 0xFF);
((SolidColorBrush)Resources["PhoneContrastBackgroundBrush"]).Color = Color.FromArgb(0xDE, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneDisabledBrush"]).Color = Color.FromArgb(0x4D, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneProgressBarBackgroundBrush"]).Color = Color.FromArgb(0x19, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextCaretBrush"]).Color = Color.FromArgb(0xDE, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextBoxBrush"]).Color = Color.FromArgb(0x26, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextBoxForegroundBrush"]).Color = Color.FromArgb(0xDE, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextBoxEditBackgroundBrush"]).Color = Color.FromArgb(0x00, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextBoxReadOnlyBrush"]).Color = Color.FromArgb(0x2E, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneSubtleBrush"]).Color = Color.FromArgb(0x66, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextBoxSelectionForegroundBrush"]).Color = Color.FromArgb(0xFF, 0xFF, 0xFF, 0xFF);
((SolidColorBrush)Resources["PhoneButtonBasePressedForegroundBrush"]).Color = Color.FromArgb(0xFF, 0xFF, 0xFF, 0xFF);
((SolidColorBrush)Resources["PhoneTextHighContrastBrush"]).Color = Color.FromArgb(0xDE, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextMidContrastBrush"]).Color = Color.FromArgb(0x73, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneTextLowContrastBrush"]).Color = Color.FromArgb(0x40, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneSemitransparentBrush"]).Color = Color.FromArgb(0xAA, 0xFF, 0xFF, 0xFF);
((SolidColorBrush)Resources["PhoneInactiveBrush"]).Color = Color.FromArgb(0x33, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneInverseInactiveBrush"]).Color = Color.FromArgb(0xFF, 0xE5, 0xE5, 0xE5);
((SolidColorBrush)Resources["PhoneInverseBackgroundBrush"]).Color = Color.FromArgb(0xFF, 0xDD, 0xDD, 0xDD);
((SolidColorBrush)Resources["PhoneBorderBrush"]).Color = Color.FromArgb(0x99, 0x00, 0x00, 0x00);
((SolidColorBrush)Resources["PhoneAccentBrush"]).Color = Color.FromArgb(0xFF, 0x00, 73, 99);
((SolidColorBrush)Resources["PhoneChromeBrush"]).Color = Color.FromArgb(0xFF, 0xDD, 0xDD, 0xDD);
}