Thanks for the comments so far. I have only paid for just over half of the work so have a decent amount left to pay, which I will only do when I am satisfied.
The planning permission states:-
"The materials to be used in the construction of the external surfaces of the development hereby permitted shall match, in type, colour and texture to those on the existing building, the approved plans and the details within Section 5 of the submitted application form. REASON: In the interests of visual amenity and in accordance with Policy EM10 of the Basingstoke and Deane Local Plan 2011-2029."
I have emailed my concerns to the builder, today, and if they disagree and say that in their view, it's fine, where is my next port of call i.e. who best to take it up with?
Some good suggestions and advice from everyone, which confirms my initial feeling that, colours aside, as I'm sure they will blend more over time, the look/quality isn't there.