How long can I stay in the sun without getting a tan?

As for race, I am not white, yet I am not black either, I’m something else lol. Anyways, me and my mother both seem to tan quite easily. And So I ask you, how long can I stay in the sun without getting a tan? I wish to not get tanner. I live in California where it’s nice and sunny =D, about 75 degrees or so here and there.

And also, will I still get the Vitamin D through the sun if the sun is shining on my sweatshirt instead of directly on my skin? or pants?

I ask this question because I am trying to get Vitamin D through the sun and not just through supplements and food.