The short answer to the color question is: The ultimate screen accurate color to buy for ANY of the first three movies is Natural Tan. The numerous whips used in those movies were all natural tan, and any differences in color we see are due to the fact that each of the whips were different ages and had been used different amounts. If you buy a natural tan whip and use it somewhat regularly, your natural tan whip will go through all the stages of aging and will at separate times look like all the whips seen in all the first three movies.
The long answer is: The whips used in all three of the films(excluding KOTCS) were all made from Natural Tan color. The problem of inconsistent colors is that not all of the whips used in Raiders were brand new when they began filming. In the original film the stunt coordinator brought his own David Morgan bullwhips to use, which were made from Natural Tan, and some were many years old, and some were fairly new. Some of those were used by Ford and the stunt men for practicing. In Temple of Doom, and Last Crusade, most of the whips from Raiders were re-used, and that is why all of the whips used in TOD and LC are consistently darker in color. If you pay close attention to the whip throughout the entire film of Raiders, you can see almost all of the shades that natural tan will turn over time at various points in the film. Here are some direct references to illustrate the different aged whips in Raiders:
In Raiders at the very beginning where Indy knocks the gun out of Barranca's hand by the water, it is a very darkened Natural, and was one of the stunt coordinator's older whips.
Then in the very next scene where Indy enters the temple (it is especially visible when he brushes the spiders off his back, as well as when he holds the whip up in the light where he says "stay out of the light") you can see that the whip is much much lighter and matches the color of a brand new Natural Tan whip. These were some of the newer whips.
As you watch the rest of the film you can see that the whips change color throughout the movie, some have been abused/distressed by the props crew with dirt etc.. but they were all made from natural tan.
Here is a quick collage of whip screen grabs from Raiders to illustrate the point:

Here is a collage of screen used whips that are now owned in private collections:

Notice that all of them have different shades of Natural Tan. Also, some of the whips in this collage are the same whip, but the pictures were taken at different times, with different backgrounds. Another thing to keep in mind is how much lighting effects the color. There are three shots of the same whip (with the pugliese tag) taken on the same date, and even taken by the same person, and the color looks different darknesses in each picture. Also, in the filming of Raiders, TOD, and LC the cinematographers used different filters, as well as different lighting throughout each of the films, and that adds to the different looks and color changes that we see on screen as well.
So to sum up in a nutshell, there is no Accurate Indy whip color except Natural Tan.
So if you buy a Natural Tan whip, the color will Screen accurately match different scenes from all three films throughout the life of the whip.
If you are wanting a brand new whip to match a specific scene then perhaps saddle tan or whiskey would more accurately match at first. But after a few years of use, it will get quite a bit darker, and not match as many of the on screen colors throughout the rest of it's life.
In my personal opinion, Saddle Tan and Whiskey never look just quite right to me when it comes to SA Indy whips, although they are beautiful colors for a non-screen accurate whip.
Something that might be fun, post pictures of your own Natural Tan whips, and be sure to include how old they are. That way we can all see how the color changes over time and with use. I have some older Natural Tan whips in my collection, and when I get an extra minute I'll post some pictures of them as well.
Regards,
Paul Nolan
www.midwestwhips.com