Small Design change to existing PHP website

I am looking at some one the is good at php and mysql. I have an existing web site that has a log in area where clients can view there on line? statements. The existing site has a black background We have built a new site that? hasn't? yet gone live. The new site? has? a white back ground. We need to take the code from the existing site and make it so when the client enters the user name and password in the new site the client area will have a white back ground and fit in with the feel of the new site.? So we need? when logging in to the? client? area from the new site it has a white back ground feel.? also when the client logs out of the admin area it should return to the new site and not the old? this is a very small job. All the code can remain where it is now we just need to change the back? ground? colour and so it fits between the new sites headers and footers when logged in.