As with all comments on this thread...CONTEXT.
Personally though, I do find it to be an insult to be called a gringa.
Honestly, most Dominicans to call you to your face gringa, unless you are very close with them and they are joking, if they call you a gringa/o I doubt they mean it in an endearing way.
If you are close to them, and they are sort of joking around with you..then it may be acceptable.
Other than that, as I said, I would consider it not the most positive way to identify/address you.