It’s tied to the “white space symbol” color. This means that if you change it and also have visible whitespace turned on, the coloring for spaces and tab characters will also change.

Note that I changed the color away from the default “orange” to “blue” in the screenshot above, for purposes of showing a change that emphasizes both the wrap symbol and the whitespace symbol more.

If I change the General Background color (to other than white) I see that the wrap symbol is white.

You must have previously changed it to white, at some point, for some reason.