Thermodynamics Question of the Day

On a hot day, does closing the blinds keep your house cooler? The thermodynamics amateur in me says no: once heat is inside the house, it's inside the house. And yet, people are always recommending this as a way of keeping inside temperatures down during heat waves. Who's right?

Next up: Does evolution violate the second law of thermodynamics? Please provide a minimum of 20 typed, single-spaced pages of word salad to justify your answer.

UPDATE: Let me be clearer. These are interior curtains/blinds. With them open, sunlight streams in and heats up whatever it touches, which is then radiated/convected into the rest of the house. With them closed, sunlight hits the blinds, heats up the blinds, and then the heat is convected/radiated into the rest of the house. Net effect: identical.

If the blinds reflect some of the sunlight back, then that's clearly a plus. But if not, then the total heat energy that enters the house via sunlight is the same either way. Or so it seems to me. But in any case, that's the question.