See the picture above? That's the average color of the universe. More precisely, if the entire sky were smeared out, the final mix would be this color, a shade of beige. To determine this, astronomers computationally averaged the light emitted by one of the largest sample of galaxies yet analyzed: the 200,000 galaxies of the 2dF survey.
The resulting cosmic spectrum has some emission in all parts of the electromagnetic spectrum, but a single perceived composite color. This color has become much less blue over the past 10 billion years, indicating that redder stars are becoming more prevalent.