Should a demo environment (in this case a trading platform) be an ugly colour in order to encourage people to move to the Live environment?
When designing a site I use standard colors (blues and grays) in order that I (and the business users reviewing the site) don't become attached to the colors. However I question the wisdom of making a customer facing demo "ugly."
The purpose of the demo is to have the user become comfortable with your site and WANT to use it. I have some experience working on trading platforms and I don't think "ugly" is a way to attract new customers.
I share the opinion, that a demonstration environment should not be ugly. Ideally, as a future customer I want to feel welcome and get to know all the features, before i consider buying anything.
Alternatively, you could reset your database at specific time intervals. These intervals should be long enough to try all functions, but too short to work productively.
You can indicate the next reset time by displaying a countdown, e.g. in one of the corners or nearby your central controls.