Tarocco rosso is supposed to have more pigmentation than other tarocco varieties...

Sounds like Bream...

Hmmm... seems like tarocco rosso isn't necessarily the most pigmented variety...

My first official graft attempt!
It's a stick of my ruby clementine on a ponderosa lemon seedling rootstock.

Yet another first attempt? You're not giving up that easy! Cleft-graft generally has a bit lower take rate, compared to other techniques. Although that shouldn't bother you, if you've done everything right, since you're not grafting hundreds of plants, where it does matter...

This first time I have been more careful than previous first times. I'm now using grafting tape that I didn't have available before. And in the mean time I have become very handy in wrapping scions also!

Good job.

One thing though, I wouldn't use lemon rootstock for mandarins or oranges. The fruit quality may suffer.

For mandarins & oranges I would use sour orange (If you don't have a citrus tristeza virus threat) or a trifoliata or a tri hybrid (swingle / citrange)

Actually I'm just trying to reproduce the ruby clementine. The fruits aren't large enough for eating anyway. If the graft takes I want to get rid of the large parent tree, so I can make more room for other, more interesting varieties!

I do have a couple of soar orange seedlings that are just about large enough, but I actually like the plants the way they are and don't really want to give them up.

The oldest poncirus seedlings I have are about the same age as the soar orange but their trunks are still too small in diameter. And this may be just me, but I think I'd rather avoid poncirus as rootstock. All the plants I have from Bachès are grafted on poncirus. Of these, the varieties with yellow fruit (femminello, yuzu) show some form of chlorosis. The eustis limequat is not from baches but is on poncirus also and has it a little too. None of the orange varieties have it though. I do know my tap water is no good for citrus but I have a feeling the rootstock has something to do with it.

I think it's your water.

You're probably right. What can I do to it?
I believe I read that a wrong pH value prohibits the roots to take up some nutrients. Could a leaf fertiliser help here?

In the mean time I placed an order at Tintori : one sfusato di amalphi and one tarocco tapi. The wife wasn't entirely happy about this!