Remember, all values are estimates from complex calculations. BeerSmith takes into account everything from your brew equipment, to temperature, to the type of ingredient and everything in between. For instance, IBU calculation can very depending on the efficiency/gravity, type of hop, AAU value and boil time based on your equipment profile, just for example. I know brewers that have switched to always just adding the same amount of hops to the batch and not paying any attention to the AAU.
You also asked about the SRM, or color of the beer. Again, this is an estimate based on calculations. If you are going by the picture on the screen, this will almost never be accurate. I say that because, unless you spend thousands of dollars on a monitor that is calibrated to true color and it is kept calibrated, colors on the screen are never true to what you would see in real life. It is more just a point of reference.
I hope all this helps.
Cheers!