Looks like you were right, according to my library. Surprised me!
Black =1940-1949 (0.15%) .2Gb's, 19 songs (2 albums)
Blue = 1950-1959 (1.26%) 1.7Gb's, 265 songs (32 albums)
Green=1960-1969 (7.33%) 9.9Gb's, 1317 songs (133 albums)
Yellow=1970-1979 (14.44%) 19.5Gb's, 2349 songs (249 albums)
Orange=1980-1989 (17.41%) 23.5Gb's, 3009 songs (285 albums)
Red = 1990 -1999 (29.56%) 39.9Gb's, 5009 songs (417 albums)
Pink = 2000-2009 (29.85%) 40.3Gb's, 5026 songs (440 albums)