I think the red fleshed trait often comes with other traits that are not desirable. The best red fleshed apples I’ve tasted are Williams Pride (barely much red flesh) and Pink Parfait and both are barely red inside. But, they do have unique and amazing flavors. Whether those traits are separable or not remains to be seen as far as I can tell. I’m really interested in maypole. It has crabby flavors going on, like high astringency, but it is very red and has a lot of really wonderful flavor. I really like eating them, but not for everyone. Rubaiyat seems more refined for it’s depth of color than average, but it has many faults such as early dropping, and going mealy. I think we are just going to have to keep making crosses to find out if we can ever get a truly stellar desert apple with deeply red flesh. My first red fleshed seedling crosses are blooming this year! Derek Mills seems to have the largest collection and so probably the most experience tasting them all. I think the general consensus is that they need improvement though. low sugar, poor texture and astringency seem to be the norm.