I noticed when cutting down a Rudy red grapefruit that I planted in a bad spot, that the sap was red.

Would using this as rootstock maybe impart itself into the scion, causing the scion to produce red blushed fruit?

Try it, it would be interesting to if it did. I often wonder how much a rootstock can effect the top growth. My interest has always been in the effect on cold hardiness, but great question.

Theres only one way to find out.

I'm trying it with some variegated Lisbon lemon as rootstock.

That has been tried very often and was never a success ...

Would be too easy ...

We shall see, I have many variegated rootstock to experiment with.

Good luck !

I wish it was that easy, then I made a variegated version of everything ..

Laaz, did you also try grafting onto Ruby Red as a rootstock? That seems like a quite interesting thing to try. I wonder if the sap is only red at the time of year the fruit colors up, or if it's red all the time?

The sap is red all the time. I haven't tried these yet, but will in the spring.