All the colors of the rainbow may not be enough for Metro's transit lines, so its Board of Directors voted unanimously Thursday to explore renaming the agency's color-coded rail and express-bus lines using letters or numbers.

Most of Metro's major transit lines are named after colors -- such as the Red Line, Green Line, Blue Line -- with one exception, the Expo Line. A report from Metro's staff states that as the system grows and new lines are added, continuing the use of colors will mean selecting names based on shades of color -- such as lime, rose, aqua, olive or lavender -- which can sometimes be difficult to decipher on maps and signage.

There currently eight rail and rapid transit bus lines in Metro's system, and the report notes that with the passage of Measure M in 2016, the agency will build and operate eight additional lines in the coming years. The report notes that Metro staff believes "the time is right" to consider an alternative naming method.

The board's action directs Metro CEO Philip Washington to return to the board in December with an implementation plan and cost estimate for changing the line names, along with marketing outreach costs to educate the public.