Hi,
I'm a UK Magento developer with many years experience. Able to talk through projects on phone/email etc.
Layered navigation (being able to choose colours, size, brand etc.) is a pretty complex beast and all depends on the store being setup correctly. If you are using a pre-biult theme then a few tweaks might be all that's in order however if you are using a bespoke custom setup then it might be slightly more tricky....
In any case I am happy to take a look and advise... When do you need this done by?
Thanks
Jake