修改为白色:

self.userNameTextField.tintColor = [UIColor whiteColor];

修改clearButton的颜色,还是用最朴素的方法比较靠谱。

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button setImage:[UIImage imageNamed:@"clear_button.png"] forState:UIControlStateNormal];
[button setFrame:CGRectMake(0.0f, 0.0f, 15.0f, 15.0f)]; // Required for iOS7
theTextField.rightView = button;
theTextField.rightViewMode = UITextFieldViewModeWhileEditing;

也有通过UIButton *btnClear = [textField valueForKey:@"_clearButton"]; 获取按钮

但是iOS11上好像并没有效果。

    UIButton *btnClear = [textField valueForKey:@"_clearButton"];
    UIImage * img = [btnClear imageForState:UIControlStateNormal];

    if (img) {
        UIImage * renderingModeImage = [img imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
        [btnClear setImage:renderingModeImage forState:UIControlStateNormal];
        //-- Add states you want to update
        [btnClear setImage:renderingModeImage forState:UIControlStateSelected];
    }
    [btnClear setTintColor:color];