I stars appear overall blue in color. Blue because contain blue supergiants which can only be young. Older stars, often approaching 10 billion years old. Groups of Pop. II stars appear overall red or yellow in color.
Old stars are red or yellow giants or red dwarfs, hence the color.
These stars contain basically no elements heavier than H and He. Contain Population II stars, from 100,000 to over 1,000,000 of them. The Milky Way has more than 150 globular clusters. Orbit the center of the Milky Way in highly elliptical orbits. I stars, typically a few hundred stars.