Really cool question! I am not entirely sure but I think I got the answer… Think of the blue food color as a ball and you have a ton of individual balls that make up your blue food coloring. Let's compare this to red food coloring which is made up of balls as well. Now the blue food coloring balls are much smaller than the red food coloring balls. They can actually travel through the white carnation stem much faster than the clunky red balls. Now this does get a little complicated as different types of blue coloring can be different sizes! I think maybe the standard blue food coloring is a smaller molecule (ball) than the red!

Science rocks!