cry the blues
1. Literally, to sing blues music or in that style. There was this old man crying the blues at the bar last night; it was a really moving bit of music.
2. By extension, to complain, whine, or express grief, especially as a means of gaining sympathy from others. Many people will cry the blues over trivial inconveniences, while millions of others silently suffer real hardships every day.
have the blues
To be or feel generally sad or melancholy. I don't know what it is, but I find I always have the blues on Sundays.
baby blues
1. A usually brief period of sadness, anxiety, and mood swings experienced by a large percentage of women after giving birth. When I had the baby blues after having my first child, I would find myself crying without knowing why.
2. Blue eyes, especially those that are light blue. I just had to ask for Sean's number after I got a glimpse of his baby blues—I'd never seen such striking eyes before!