One simple way to tell which is correct is to remember that **deleting an orbit of white nodes from a valid Satake-Tits diagram should give another valid Satake-Tits diagram**. If the node you are asking about (which is node number 2 in Bourbaki's labeling) were white, then removing one of the other white nodes would give a supposed Satake-Tits diagram for $D_5$ which is not possible, whereas if it is black we get the diagram for the real form of $D_5$ for a real quadratic form with signature $(1,9)$.

For more explanations on the subject, I recommend Tits's 1966 survey paper, "Classification of algebraic semi-simple groups" (in *Algebraic groups and discontinuous subgroups*, Boulder 1965, *Proc. Symp. Pure Math.* **9** 33–62, p.372ff in volume 2 of the EMS edition of the complete works of Tits), see in particular §3.2.2 (keep in mind that what Tits called a "distinguished orbit" is an orbit of white nodes, and what Tits calls a "Witt index" is what is now generally called a Satake-Tits diagram). The possible diagrams over any field are given in the appendix tables of the paper in question, with a specific mention of which are realized over $\mathbb{R}$.

Another independent confirmation is Araki's 1962 paper "On root systems and an infinitesimal classification of irreducible symmetric spaces" *J. Math. Osaka City Univ.* **13** 1962 (1–34), which proceeds to derive the classification of simple real lie Groups directly from the Satake diagrams without using Cartan involutions. The diagram you seek is on page 29.

(I was about to also refer to Tits's 1967 book *Tabellen zu den einfachen Lie Gruppen und ihren Darstellungen*, which contains fewer typos than Onishchik and Vinberg, but I'm surprised to find that he does not give Satake diagrams nor any information from which the answer could be obviously derived, such as the real rank of the real form.)