If you are using the bed as a 20 year cure, the blue would represent the still water. Remember, though, that Marie recommends not using too much water in a bedroom, as it can easily become too yang.
If you are looking at the general space feng shui, the South is activated with fire. For that reason, I would check to be sure you aren't adding too much still water energy.
Remember that you can weaken water with wood or control it with earth. Experiment until you find the right balance of the elements. You can either use muscle testing, dowsing, or just tune into the feeling of the area until you come to a sense of balance.
All the best!