Couldn’t UIToolBar be transparent?

To make a completely transparent toolbar, use the method described here. In a nutshell, create a new TransparentToolbar class that inherits from UIToolbar, and use that in place of UIToolbar.

TransarentToolbar.h

@interface TransparentToolbar : UIToolbar
@end

TransarentToolbar.m

@implementation TransparentToolbar

// Override draw rect to avoid
// background coloring
- (void)drawRect:(CGRect)rect {
    // do nothing in here
}

// Set properties to make background
// translucent.
- (void) applyTranslucentBackground
{
    self.backgroundColor = [UIColor clearColor];
    self.opaque = NO;
    self.translucent = YES;
}

// Override init.
- (id) init
{
    self = [super init];
    [self applyTranslucentBackground];
    return self;
}

// Override initWithFrame.
- (id) initWithFrame:(CGRect) frame
{
    self = [super initWithFrame:frame];
    [self applyTranslucentBackground];
    return self;
}

@end

(code from the blog post linked above)