Ive just been through this when Thaiwatsaduk mixed 9 litres of wrong paint.
Had my phone in front of them and showed them to 2 colours we wanted.
Light grey and off white.
We get home and the light grey was correct but the off white was dark grey.
They said they cant change it cause it's already mixed. I said you mixed it wrong not me.
Again showing the colours on my phone asked how the F is this dark grey off white?
They said I have to pay again at ฿2,400 for the off white. Lost it with them again and they come back with, OK we will give you 9 litres of off white but can you pay ฿400 extra and you keep the dark grey?