Blue Highlight around Custom NSButton - objective-c

Question

I want to make a custom NSButton with a solid color for its background but there is this blue highlight around the button that I can't figure out how to get rid of. Does anyone know how to get rid of it?
Thanks!
EDIT:
Here's the code for the button:
#implementation ZDButton
- (id)init {
if (self = [super init]) {
self.title = #"";
self.isSelected = false;
[self setBordered:NO];
[self setBackgroundColor:[NSColor whiteColor]];
}
return self;
}
- (void)drawRect:(NSRect)dirtyRect {
[super drawRect:dirtyRect];
[[NSColor colorWithCalibratedRed:arc4random_uniform(100) / 100.0
green:arc4random_uniform(100) / 100.0
blue:arc4random_uniform(100) / 100.0
alpha:1.0] set];
NSRectFill(dirtyRect);
NSDictionary *att = nil;
NSMutableParagraphStyle *style =
[[NSParagraphStyle defaultParagraphStyle] mutableCopy];
[style setLineBreakMode:NSLineBreakByWordWrapping];
[style setAlignment:NSLeftTextAlignment];
att = [[NSDictionary alloc] initWithObjectsAndKeys:
style, NSParagraphStyleAttributeName,
[NSColor whiteColor],
NSForegroundColorAttributeName, nil];
int width = [self.title sizeWithAttributes:att].width;
int height = [self.title sizeWithAttributes:att].height;
int x = (dirtyRect.size.width - width) / 2;
int y = (dirtyRect.size.height - height) / 2;
NSRect centeredText = NSRectFromCGRect(CGRectMake(x, y, width, height));
[self.title drawInRect:centeredText withAttributes:att];
}
#end