From the Menu Bar select Options, then Colour Preferences to open the Colour Preferences window.

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Here you can change the background colour of various areas of the application.

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Click on the colour that you want to change to open the standard Windows colour pallete to make the change.

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Click on the Default settings button to return all the areas back to their default colours.

 

Click on the 'Dark theme' button to change a number of the colours at once to a pre-set dark theme.