I need a graphic designer to make my html 5 forms application look beautiful

I run a small software company. We built rich internet applications using html 5 These applications record customer profiles.

We have built 10+ systems which function very well, but look bland and boring. I need a designer to come and add the "wow"factor to our applications. I need an expert designer to add the colour and graphical assets that will lift our apps and make them look gorgeous while maintaining ease of use. In short, make them beautiful to look at and use.

I have a team of developers, so the focus is absolutely on design, rather than coding

The output will be a series of mockups that I can pass to the front end developers for implementation.

I need a design that works well with different colours (essentially, we will take the primary colour from that customers logo or brand, and use that in the new design).

Remote working via Skype, WebEx expected with possible face to face.

In terms of duration, not sure. How long does it take to create a beautiful UI?

Can you help?