NZXT Switch 810 PSU Help!

Specs of the system ?
See if this one is enough for you : http://www.scan.co.uk/products/600w-ppc-silencer-mkiii-...

There's this one if you need more juice : http://www.scan.co.uk/products/750w-nzxt-hale90-750m-mo...

Both are quality psus.

Let me be more specific, 750w at the least and if the psu box is white then I want the cable to be only black none of that yellow, orange red cable showing if that makes sense.

This is your best bet : http://www.scan.co.uk/products/750w-nzxt-hale90-750m-mo...

High quality psu with your theme color with 750W and modular, also of the same brand as the case.

http://www.scan.co.uk/products/corsair-psu-hx-and-txmod...
How about these cable with this
http://www.scan.co.uk/products/750w-corsair-pro-series-...

Spending so much on white cables, i don't see the point, when the psu will give a color contrast, either get one of the nzxt hale psus or don't bother and get a normal psu within 750W, the corsair hx 750 is now made by channel well and it has been reported with clicking noises.

My build is white/black contrasting colours, what about the Txm series psu from corsair like the tx750m?

TXm series is a bronze unit and also made by channel well, but there's no report of clicking noises, both are good psus either the hx750 or tx750m.
You'll still have black cables(for the motherboard), either the hx or tx are semi modular.

The Txm have white/blue/red modular cables that you can buy separately for about £40

Well it's your choice, if you want white modular cables, if you do the right cable management, you'll not notice it, and it depends on how much cables you're going to use in the system(cards, hdds,ssds,etc.).
The nzxt hale90 is still a good option or this psu(without color match) : http://www.amazon.co.uk/dp/B00305I3ZQ/

Or if you want a fully modular psu from corsair : http://www.ebuyer.com/227503-corsair-850w-ax850-modular...