Why is Cyanidine soluble in water?
Cyanidine actually looks to me to be a rather highly polar compound. It's essentially a $\ce{C15}$ hydrocarbon having 5 hydroxyl groups and a formal positive charge.  

The ratio of hydroxyl groups to the number of carbons is the same as that of water-miscible isopropyl alcohol. (Of course smaller molecules like isopropyl alcohol also tend to be more soluble than larger molecules.)  

The most important feature indicative of it's rather high polarity and water solubility is it's formal positive charge. This is analogous to placing a positive charge on a large amine by protination in order to turn the amine into a polar, water soluble compound.