These are flavors I used for each color:
Red soda -- Strawberry soda
Blue ---------Jones Soda Co. has blue soda but if not, 7-Up with a few drops of blue food coloring added. see note*
*Be sure to use water-based food coloring so it blends completely.
(For the pictures, I used Izze Blueberry soda and added some blue food coloring. I think 7-up might work better.)