Blondes have more fun but brunettes get more respect. I'd say go by your personality/age and don't forget your wardrobe... Will your clothes look better with blonde or brown?
For high-contrast, you can choose a dark color like purple or dark brown/chocolate. For a more neutral look, white or cream looks good, or even champagne. Sort of depends on the time of day or occasion...
Like it was suggested, your baby could have either blonde or black hair. But I know a couple in a similar situation and their child's hair is brown.
Here is a page with pictures of hairstyles for women over 50 including short hairstyles. Scroll down the page and click on the thumbnails.