From the Preferences screen select "Appearance"
To change the colour scheme of the application simply use the drop down list and click Apply. The change will be immediate.
In general the Dark Theme is used for low light conditions and the Bootstrap theme for higher contrast. The Lite Theme works well in office lighting conditions.
When using MultiBit HD in a public place or other situations where you may be observed it can often be desirable to hide the large font balance information. To switch between them just select from the drop down list and click Apply. The change will be immediate.
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