macOS set the background colour of an individual NSTableColumn

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What I want to do is basically explained in the subject, I want to set the background colour of a table column to be different from the other columns in the table.

I have been told here to use:
-(void)tableView:(NSTableView *)aTableView willDisplayCell:(id)aCell forTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex; and that is working fine on the same table to set custom text colours, however it isn't working correctly for setting the background.

Below is my code.

- (void)tableView:(NSTableView *)aTableView willDisplayCell:(id)aCell forTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex{
	if([aTableView isEqualTo:spellClassLevelTable]){
		if(![aCell isKindOfClass:[NSTextFieldCell class]]){
			return;
		}
		if(![aCell respondsToSelector:@selector(setTextColor:)]){
			NSLog(@"error, cell doesn't respond to selector setTextColor:");
			return;
		}
		if(![aCell respondsToSelector:@selector(setBackgroundColor:)]){
			NSLog(@"error, cell doesn't respond to selector setBackgroundColor:");
		}
		//if the current cell is in the selectedRow and the table is the first responder it should go white.
		if([aTableView selectedRow]==rowIndex && [[[aTableView window] firstResponder] isEqualTo:aTableView]){
			[aCell setTextColor:[NSColor whiteColor]];
		}else{
			[aCell setTextColor:[divArcOrDom transformedValue:[[spellClassController arrangedObjects] objectAtIndex:rowIndex]]];
		}
		if([aTableColumn isEqualTo:[[spellClassLevelTable tableColumns] objectAtIndex:0]]){
				[aCell setBackgroundColor:[NSColor erLightGrayColor]];
		}else{
				[aCell setBackgroundColor:[NSColor yellowColor]];
		}
	}
}

 

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Anyone?