I'm trying to change the back button arrow

I'm currently using the following to control the text size as well as the text color on the back button:
[[UIBarButtonItem appearance] setTitleTextAttributes: [NSDictionary dictionaryWithObjectsAndKeys: [UIColor whiteColor], UITextAttributeTextColor, [UIFont boldSystemFontOfSize:16.0f], UITextAttributeFont, [UIColor darkGrayColor], UITextAttributeTextShadowColor, [NSValue valueWithCGSize:CGSizeMake(0.0, -1.0)], UITextAttributeTextShadowOffset, nil] forState:UIControlStateNormal]; but if I want to change only the arrow's color for the back button, what should i do?