That's what I get opening the topic on a forum...

FYI the whole idea is to screen and weed women out with bad qualities. Not invest your emotions in the wrong woman (LTR wise.) Minimize your losses. If you disagree...then your clearly on the wrong forum.

The red flags:

-Never had a BF until 30. Only casual sex and a few ONS.
-Dating a black guy and having a preference for (...) black guys are two different things.

We have to assume the womans sexual history is much than what she leads on to. Investing emotionally in a woman who's or promiscuous or statistically a high infidelity risk...bad idea.

the color of the d@ck means nothing..
maybe she went black because she likes it big.. that's just personal taste/preference of the girl. Nothing to judge there.
if you are not insecure about your size why should it matter if a woman has been with a black guy or two?
There is one thing that maybe can make a guy insecure and that's black guys tend to be quite good in picking up women and if she is used to guys who do it effortlessly then she might lose interest if you can't keep up with the previous guys.

@op if you want to screen if she is relationship material don't look into her sexual past. Check for issues in her personality. But first work on your inner game. You are too much worried.