u can create image like this, hope this helps u ..
NSImage *blackImage = [[NSImage alloc]initWithSize:NSMakeSize(22, 12)];
[blackImage lockFocus];
NSColor *blackColor=[[NSColor blackColor]autorelease];
[blackColor set];
NSRectFill(NSMakeRect(0, 0, 22, 12));
[blackImage unlockFocus];
[item setImage:[blackImage autorelease]];//now you can get the black image hear item is imageView this is without ARC code u can remove autorelease if u want