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Smart windows are designed so they let in light and heat during the day, but during the night they automatically change in properties to prevent heat from escaping from the colony.
These windows may or may not be transparent at night.
Studies have shown that smart windows may provide all the heating needed for a Martian base.
A low tech solution (which may be possible with early Martian industry) would be to use motors on a timer to cover windows with an insulator at night.
(Note: some people call transparent solar cells that allow a window to generate power 'smart windows'. That is not what we are discussing here, heat management is the key idea.)