BlueDingo said:
You can have green stars. Just chuck a shitload of copper sulfate at it and it will burn green until the copper sulfate runs out.

Might not be good for the star. Some elements are known to speed up the star's aging. Did you know iron is extremely deadly to a star. A common joke among some scientists is that the best thing to kill the sun with is your own kitchen.

Though if you want the star to be green or purple, you could try a planet with a magenta atmosphere, which would give you a star that appears green, like how Sol looks yellow but it's actually white, and we just get tricked into not seeing the blue because of the sky.