Do I need expensive shampoo for coloured hair

[Bodicea]

I have always used what ever shampoo is on offer in the supermarket. Think herbal essences, Pantene, treseme etc.
My hairdresser keeps telling me i need to buy the posh expensive stuff especially as I have more recently had more colour put into my hair. I have always thought expensive shampoo conditioner is a waste of money.
Is she right? I don't trust her opinion as I know she wants to sell me stuff. Do I need to cough up or is it all a load of branding nonsense? After all hair is dead cells at the end of the day so surely vitamins etc are not mugh use!!!
Feel free to correct me and recommend something that will care for my highlighted hair.

For highlighted hair, uv protection might help stop it changing in the sun.
It it's dryer, conditioning might help.
But no, I don't think you need more expensive shampoo.
I use Lush and my hair is in great condition. I use DaddyO which stop fair hair going brassy however I don't not actually colour my hair anymore.
I think some shampoos feel nice and smell nice. I had my hair cut in Toni & Guy this week (impulse, I was walking past) and I like their salon products and try smell gorgeous. But I don't buy them because I prefer Lush's products. Which also smelt divine. Price wise they are not that much different Rjough Lushs shampoo bars are cheaper and last for ages.
Hairdressers who get profit from products they sell have an agenda, so just buy what you like.

All the brands you mention have an option for coloured hair. I just use them and only buy when they are in offer!