Should you be concerned if your 4-year-old daughter draws very gloomy pictures?

I wouldn't read to much into it, but if you are concerned then sit down and ask her what the picture is about, ask he if it's a sad picture. Ask her if she feels sad, you don't want to make her think she is doing anything wrong, just give her brighter colours even suggest 'happy' pictures, but don't overly interfere, I'm sure it's nothing.