Symbol You Want on Color You Want!
I was looking for this answer for days and here it is the right and easy way to create a custom marker:
'http://chart.googleapis.com/chart?chst=d_map_pin_letter&chld=xxx%7c5680FC%7c000000&.png' where xxx is the text and 5680fc is the hexadecimal color code of the background and 000000 is the hexadecimal color code of the text.
Theses markers are totally dynamic and you can create whatever balloon icon you want. Just change the URL.