The Sixties were a pretty sunny decade when it came to pop music, as these relatively obscure tunes demonstrate:
The Millennium: Some Sunny Day
[purchase]
Skeeter Davis: Summer Sunshine
[purchase]
Hearts And Flowers: Try For The Sun
[purchase]
See also: Margo
Further research: The Millennium: here and here, Skeeter Davis: here, Hearts And Flowers: here and here.