Colour changes are usually attributable to temperature but can also be from changes in light as well. Temperature can affect on flower colour. Flowers that were red in previous years were faded in this year
Look at the leaves on your two photos.the leaves in the right photo appear to be a much deeper green than the left one. To me that would suggest the plant received a good deal less light last year, thus the darker more vibrant bloom colour. The more light this year probably washed out some of the colour.