Six color groups in the standard Monopoly board game contain exactly three properties.
The three-property groups are light blue, pink, orange, red, yellow, and green. Each of these groups requires a player to acquire three matching properties before building houses or hotels. The remaining two groups have only two properties each: the dark-purple group and the dark-blue group.
This gives the classic board eight color groups in total and 22 street properties overall. The distinction matters strategically because completing a three-property group is usually harder than completing a two-property group, although the potential rental income and development patterns vary substantially by group.
Railroads and utilities are not color groups. They are separate property categories, so they do not change the count of six. Special editions can alter names, colors, or layouts, but this count applies to the standard American Monopoly board.