How to set flat style to NSButton on NSToolbar (to look like NSToolbarItem)

Question

How to set flat style to NSButton on NSToolbar (to look like NSToolbarItem).

For instance, the last toolbar item in the figure (Pointer) should look like other toolbar items. Currently it has border with shadow. How to make it flat. Prefered language Objective-C.

Need to find proper styles to adjust NSButton to look like NSToolbarItem. NSButton is created on this way:

- (instancetype)initWithImage:(NSImage*) image
{
    self = [super init];
    [super setImage:image];
    //[super setBordered:NO];
    popover = nil;
    return self;
}

If I include code with [super setBordered:NO]; then I get proper visuals, however when I set new image it doesn't refresh. Only after second clicking new image is visible. So, after calling

[button setImage:newImage];

button doesn't refresh. Label is always refreshed.