I'm a North African Jew who lies in Canada.  BY LAW, persons of North African and West Asian descent are to define themselves as 'White' on the American and Canadian census since 1975.  You are as White as Arabs, Berbers, Turks, Greeks, Armenians and Persians.  If you're Ashkenaz you're of European descent and have been legally 'White' in America since the 1950s.

If you are living in the majority of European countries you would be legally non-White, the same as Roma, Sinti, or Turkish peoples in Europe.

Culturally, if you're just discovering that you might not be White - you're most likely White  The anti-Semites who hate White people will consider you White and the anti-Semites who revere Whiteness will regard you as non-White.  Given that Yom HaShoah was last Wednesday it shouldn't be THAT much of a surprise.

NO, you are not a person of color if you are white.  You are still a white person in their eyes.  This means they hate your twice as much.

I'm Jewish from Israel (Middle East), does that make me by definition (specifically as defined by the USA) a person of color?

Is your skin white? No? Then yes. Yes? Then no.

If I have a white skin and not from the USA, am I still defined as a person of color?

You're a blanco, yes.

until I heard the term "Person of Color" as a pre-defined term used to "segregate" anyone who isn't white

Talking opposites, White can refer to a combination of all colors while black the absence of any specter of light, therefore the lack of color. So when we're talking about white people we may be talking about humans with all the colors on them, rather than segregate they seem to include. Fascinating ain't it?