Is just a true white balance you are after? And by saying "accurate" what exactly do you mean?
Firstly, why don't you set the white balance on your camera manualy before every shooting? I always carry a grey card with me, take a picture of it so it fills the frame and tell the camera to use that as reference to choose the white balance. This is different in each brand or model, for Canon it's in the second camera menu/custom white balance, choose the photo of the grey card and then set your white balance as custom. I don't know how to do this for other branded cameras, but this always gives you accurate white balance for every occasion.
When you would like to capture an "accurate" photo, I suppose you mean to capture it like you see it, right? Well, there are many problems there, not just white balance. The most prominent one is the difference in Dynamic Range between your eye sight and a camera sensor. In simple terms, your eyes can "see" a greater range of grey between shadowed areas and brightly lit areas than your camera can. So, your camera will capture pure black a long before your eye starts to loose all information on that spot. So what to do about that? Well, HDR, or High Dynamic Range Photography. But isn't that editing? Well, you edit just to present it as "accurate" as possible. But is accuracy really what you are after? Isn't bending reality part of the art of the photographer. If you chose to capture realistic photos, then you would only use 50mm lenses (in 35mm equivalent) That's the closest to our eyes "sharp focus area". But presenting the viewer something that he/she is not used to, like an ultra-wide-angle photo, captures the imagination, and makes the photo pleasant and extraordinary. Same with the compression of furthest objects with a long telephoto.
So, what if your white balance is off? It doesn't mean that it's wrong! I sometimes intentionally play with the white balance to give a more pleasing result. This is an example of a photo that gives different results by just changing the white balance. First one almost gives a feeling of moonlight on a beach, the second one gives a feeling of harsh summer sunset!