The policy is written on the back of your receipt and it doesn't state you have a right for an exchange. In the UK, exchange and refund of non faulty goods is a privilege, not a right. It is always subject to store's discretion. Employees from head office or other SAs don't set the policy, nor do they all fully understand how concessions operates. And none of them have to worry about HoF H concessions sales target.
You are not throwing 2 X £4570 if you return the green L to Harrods. You get your money back almost instantly.
And I can see why the HoF in Glasgow has a different client base compared to Harrods. Harrods is a large store with high volume of clients, a lot of them are tourists who prefer brighter colours. Glasgow is a LOT less touristy and serves mainly local customers who in general prefer conservative styles.
The bottom line is, is it good customer service? Probably not. But is it against H policy? I don't think so.
Agree totally w/ XiangXiang! Great post.