Looks like we have found a compromise.
On desktop, right click and personalize (as per creese's post).
Then towards the bottom of the screen where it shows your selected theme items, click window colour, then advanced appearance settings.
On the item drop down list select 3d objects, Click on colour 1 and then play around with the custom colour palette for a while, applying and checking back in Sims .net.
You may also have to change Inactive title bar to the same custom colour. Happy mixing