Yes, we can expect third strain to contain more of blue, tan and red.
Blue (collinear back bone common to both)
Tan (the positions of their specific sequences at the same location), and
Red (the positions of O157:H7 specific sequences).
TaxPlot tool is used for comparing the query proteome with two other dissimilar species to acquire a three-way comparison. The proteins sequences which have highest similarity with the second genome are then compared with third genome using this tool.
Proteins from the third proteome, which are identically similar to other two reference proteomes, are considered and are drawn through the diagonal. A query protein which shows more similarity with particular reference proteome comes close to the axis to represent that particular proteome.
So, the protein sequences, which are more similar, are identified by this tool. The genes that are transferred horizontally from a distant organism are also identified using this tool.