How to avoid UIToolbar's tintColor to change UIButtonItem button color?

In iOS7,I Created a UIBarButtonItem and init with a image which color is green.But the final appearance of that UIBarButtonItem's image is a image with the same shape but different color.The color was changed to blue.

The code is below:

_recordVoiceItem = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"voiceIcon"] style:UIBarButtonItemStylePlain target:self action:nil];

    _textView = [[UITextView alloc] initWithFrame:CGRectMake(40, 4, 220, BOTTOM_BAR_HEIGHT - 2*4)];
    _textView.layer.borderWidth = 1.f;

    _rightItem = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"modeIcon"] style:UIBarButtonItemStylePlain target:self action:nil];

    _bottomBar = [[UIToolbar alloc] initWithFrame:CGRectMake(0, self.view.frame.origin.y + self.view.frame.size.height - BOTTOM_BAR_HEIGHT, self.view.frame.size.width, BOTTOM_BAR_HEIGHT)];

    _bottomBar.items = @[_recordVoiceItem,[[UIBarButtonItem alloc] initWithCustomView:_textView],_rightItem];

    [self.view addSubview:_bottomBar];

And I have tried to create a UIToolBar and add some items to it through Interface Builder.The appearance is fine. The color of the UIBarButtonItem's image was the origin image's color.

I doubt that I need to add some code to set some properties of the UIToolBar or UIBarButtonItem if I want to it through writing code. Could you tell me how to do?