Very likely not the last in this series, as I have grown very fond of the theme (the 5th is already underway).
#4 was photographed in natural (northern) light emanating from the right, which is why there is a distinctly darker red on the left of the painting. Of course, taking a photo in this way makes it a ‘truer’ image, since that is how it would look should it be hung in a similar location. The only photoshopping done was to crop the image.
*edit to add* I just noticed that small black dot on the upper blue arc. It was a fruit fly and I blame the peaches.