The blossom color of many tree species is influenced by many factors. These include soil conditions such as pH and moisture level, atmospheric temperatures at the time of bloom, humidity levels, general tree health and nutrition.

In these Photoshop days, the temptation to enhance the appearance of plants is apparently irresistable to many sellers. The best you can do is to consult a book like Michael Dirr's Manual of Woody Landscape Plants and use this information to select the dogwood variety which will at least have the potential for the reddest flowers.

Thank you for the book suggestion. Being new to gardening, it never even crossed my mind all those factors would effect bloom color. I knew they would effect plant size, how much or even if they bloomed...but I did take for granted that if they bloomed, the color would be "the color". It makes since that richness of the bloom color could be effected also.

We had a pink dogwood (variety unknown) at a previous house, and I also found that the color of the bracts depended some on the age of the bract. Newly opened, the bracts had a richer color, a deep pink, and by the time they dropped some of the color was quite a bit paler, though still pink.

FWIW, ours was on the south side of the house (in part shade from some large oaks) where we looked through it toward the east morning sun. The newly unfolding leaves were reddish in color, and with the morning sun through them, glowed until they were mostly unfolded and turning green. It was a lovely unanticipated benefit that was at least at decorative as the blooms for the couple of weeks that it occurred each year.

The suggestion of Dirr's book is a good one; it's a reference that I use often, and I like his writing style. However, he tries to be as complete as possible, so on a practical level, not all of the varieties that he mentions may be readily available in commerce, so you'll have to investigate that as well as finding varieties that sound to meet your requirements.