It appears that Blue is the dominant trait.
Let "B" be the gene for Blue and "b" be the trait for yellow.
Since Blue appears in all generations and in combinations with two blue parents, Blue is dominant and yellow is recessive.
Traits are typically discussed in pairs of BB, Bb, or bb. A dominant trait will be present in either paring of BB or Bb. A recessive trait will only show in bb. Each child will have a 50% of being Bb, a 25% chance of BB, and a 25% of being bb. This means a child has a 75% chance of being blue and a 25% chance of being yellow.
As these are individual rolls and not statistical, it is okay to have a wider spread of bb Yellows than Blues so having 2 yellows and a blue is probable.
In order for each tree to be valid, Parents A and B must both be carriers (Bb at least) of "b" genes. BB will not produce that child. Parents that are both Bb/Bb, Bb/bb, or both bb are valid
In the case of C, D, E, F, J, and K at least one member in each paring must be a carrier of "b". As all their children are Bb in order to both be Blue and produce Yellow offspring. A combination of BB/Bb, Bb/Bb or BB/bb is possible, with the latter more likely to produce the genes present in their grandchildren. They cannot be BB/BB or bb/bb.
Please note that this cannot be reversed as while the lines increasingly favor Yellow, a Blue cannot both be recessive and produce a child of either color. A child of a bb/bb will always be yellow. For blue to be recessive, than all children of L and M will be blue. Also while this is basically how phenotypes work, sometime the coloration is controlled by two or more genes.
For example, human hair has two genes, one which controls Dark vs. Light and the other which controls Red vs. Light and depending on the parents can run a gamut of colors.