searchBar去初灰色边框，以及设置searchBar placeHolder字体的颜色和大小

1、去除灰色边框

self.mySearchBar.barTintColor = [UIColor whiteColor];

self.mySearchBar.layer.borderWidth = 1;

self.mySearchBar.layer.borderColor = [UIColor whiteColor].CGColor;

self.mySearchBar.layer.cornerRadius = 15;

self.mySearchBar.layer.masksToBounds = YES;

self.mySearchBar.backgroundColor = [UIColor clearColor];

2、placeHolder字体的颜色和大小

UITextField * searchField = [self.mySearchBar valueForKey:@"_searchField"];

[searchField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];

[searchField setValue:[UIFont boldSystemFontOfSize:13] forKeyPath:@"_placeholderLabel.font"];