I understand that a Hubble diagram is a graph of recession velocity plotted against distance for distant galaxies, and shows a linear relationship. The Hubble constant is the gradient of the graph. We are now observing extremely distant galaxies with greater than expected velocities due to 'dark energy'. Does this mean that if we plotted these galaxies on a Hubble diagram, the graph we plot would no longer be linear, and the gradient would become steeper the further out we go? Thanks.