The latest version of WordPress has a drastically different colour scheme than previous versions. If you don’t like the dark design, there are a few ways to change the colours and the styles.
To change the WordPress theme to one of the colour schemes that come packaged with 3.8, go to Users > Your Profile and select one of the 8 options.
If you want more options, you can also download and install the Admin Color Schemes Plugin. This will give you 8 additional colour schemes.
I’m using the “Light” theme. It looks closest to the old version of WordPress.