Set the white balance to match the light and you'll get better results. Auto is not a light source. It's just the camera's way of guessing, and not only is it unnecessary most of the time but it's usually several hundred degrees Kelvin off. Even if there's white in the scene, it usually contains some color cast, from the sky if nothing else, and therefore is unreliable as a WB target in auto or post. I can't advise auto as a solution when you know the light source. If the barn is lit by the sun, set the WB to sun. If it's lit by a tungsten light bulb, set it to light bulb. If you want to be more accurate, place a white card in the same light as the barn. Then you can use it for a custom WB or simply select it in post for accurate WB (which works better in RAW). However, note that if you're shooting sunrise or sunset, you don't want to do custom WB because that will neutralize the golden hue of the light. You want to leave WB at daylight during those hours to preserve the natural colors.
Guessing actually adds difficulty in processing. Yes, if you shoot RAW you can select any WB in post, but that's just guessing. Without a known color-neutral target in the frame, you'll struggle with sliders and trying to remember what the scene looked like, which is even worse if your monitor isn't calibrated. With custom, you know it's correct without guessing. When using a white card, it should be something like the ColorChecker from X-Rite. Some exposure gray cards actually have a color cast that won't help with WB.
Hallmarks of professional photography include being exact, consistent, organized and making things repeatable. Auto WB qualifies as none of those things. Even under the same light, auto can change depending on where you point the camera, and so you could have 100 images under the same light each with a slightly different WB, making it even harder to figure out which is correct in post. Auto can be a handy tool, as sometimes there's no other way to pinpoint the light temperature. That still means more work in post. However, if you compare a series of different scenes shot in auto to the same scenes shot in custom or preset, the custom or preset will look better to most people. Auto appears to be OK in the viewfinder and when not compared to anything else, but when you put it against custom or preset, it's rarely as accurate. If you have the time, try to match the WB exactly to the source.