The color of the stars. Other answer(s) explain a situation where the observer is in our Universe, but not in the Earth. You ask for stars which are wrong and it is clearly visible that it can not be our Universe. Thus, the stars on the sky must look somehow from which already an educated layman can say, it can not happen.

If only the constellations differ, that can happen anywhere - already a ten light years away most constellation becomes unrecognizable. If the milky way looks differently, galaxies are visible in the sky, or there is more and lesser stars - these all can happen inside our Universe, only in different places.

However, what can not happen, that is the color of the stars. The stars are plasma, with a roughly black-body temperature spectrum (not exactly but the difference is not visible for us). Thus, their temperature can affect their color, but it can not be any color. How a human free eye sees a star, that depends on its temperature and it can not be any color, only one of this line:

Thus, a star can be red, orance, yellow, white or light blue. No star can be green, blue or purple. It is impossible. At least, in our Universe.

P.s.1: if you see the sky, you will see that most stars are white or yellow. That is because most stars we see, are roughly Sun sized. There are some exceptions and with a good eye, on a clear sky you can see it.

P.s.2: There might be rare phenomenona, like having an oxygen nebula around the star, which can make a star green. But that is rare. It can not happen in all stars.

The color of the stars. Other answer(s) explain a situation where the observer is in our Universe, but not in the Earth. You ask for stars which are wrong and it is clearly visible that it cannot be our Universe. Thus, the stars in the sky must look somehow from which already an educated layman can say, it cannot happen.

If only the constellations differ, that can happen anywhere - already at ten light years away, most constellations become unrecognizable. If the milky way looks different, galaxies are visible in the sky, or there is more or fewer stars - these all can happen inside our Universe, only in different places.

However, what cannot happen is certain colors of the stars. The stars are plasma, with a roughly black-body temperature spectrum (not exactly, but the difference is not visible to us). Thus, their temperature can affect their color, but it cannot be any color. How a human free eye sees a star, that depends on its temperature. It cannot be any color, only a color along this line:

Thus, a star can be red, orange, yellow, white or light blue. No star can be green, blue or purple. It is impossible. At least, in our Universe.

P.S.: if you see the sky, you will see that most stars are white or yellow. That is because most stars we see are roughly Sun sized. There are some exceptions and with a good eye, in a clear sky you can see it.

P.P.S.: There might be rare phenomena, such as having an oxygen nebula around the star, that could make a star green. But that is rare. It cannot happen in all stars.

The color of the stars. Other answer(s) explain a situation where the observer is in our Universe, but not in the Earth. You ask for stars which are wrong and it is clearly visible that it can not be our Universe. Thus, the stars on the sky must look somehow from which already an educated layman can say, it can not happen.

If only the constellations differ, that can happen anywhere - already a ten light years away most constellation becomes unrecognizable. If the milky way looks differently, galaxies are visible in the sky, or there is more and lesser stars - these all can happen inside our Universe, only in different places.

However, what can not happen, that is the color of the stars. The stars are plasma, with a roughly black-body temperature spectrum (not exactly but the difference is not visible for us). Thus, their temperature can affect their color, but it can not be any color. How a human free eye sees a star, that depends on its temperature and it can not be any color, only one of this line:

Thus, a star can be red, orance, yellow, white or light blue. No star can be green, blue or purple. It is impossible. At least, in our Universe.

P.s.1: if you see the sky, you will see that most stars are white or yellow. That is because most stars we see, is roughly Sun size. There are some exceptions and with a good eye, on a clear sky you can see it.

P.s.2: there might be rare phenomenon, like having some oxygene nebula around the star, which can make a star green. But that is rare. It can not happen in all stars.

The color of the stars. Other answer(s) explain a situation where the observer is in our Universe, but not in the Earth. You ask for stars which are wrong and it is clearly visible that it can not be our Universe. Thus, the stars on the sky must look somehow from which already an educated layman can say, it can not happen.

If only the constellations differ, that can happen anywhere - already a ten light years away most constellation becomes unrecognizable. If the milky way looks differently, galaxies are visible in the sky, or there is more and lesser stars - these all can happen inside our Universe, only in different places.

However, what can not happen, that is the color of the stars. The stars are plasma, with a roughly black-body temperature spectrum (not exactly but the difference is not visible for us). Thus, their temperature can affect their color, but it can not be any color. How a human free eye sees a star, that depends on its temperature and it can not be any color, only one of this line:

Thus, a star can be red, orance, yellow, white or light blue. No star can be green, blue or purple. It is impossible. At least, in our Universe.

P.s.1: if you see the sky, you will see that most stars are white or yellow. That is because most stars we see, are roughly Sun sized. There are some exceptions and with a good eye, on a clear sky you can see it.

P.s.2: There might be rare phenomenona, like having an oxygen nebula around the star, which can make a star green. But that is rare. It can not happen in all stars.