Android 5.1 Lollipop has more to offer than people likely realize, even if it isn't as monumental of a change as what was seen inside of Android 5.0 when coming from Kit Kat. Some of the changes are a little more obvious while some are a bit more subtle and could easily be missed if users weren't paying close attention. The latest of details being highlighted are the fast scroll bars, which are the little bars on the side of the screen edge (like in your contacts list for example) allowing users to move through lists of Alphabetical contents more quickly. Even minor details deserve some attention, and that's just what Google has done here.
As you can see from the two images below courtesy of Android Police, the fast scroll bar from Android 5.1 Lollipop is a little more pronounced and should feel easier to interact with. This would be due to the slightly larger size of the gray bar as well as the colorful little piece denoting the position that now connects to the big indicator with the letter on it. Both the green indicator bar and the gray bar that it travels on are also more squared off in 5.1. In contrast to Android 5.0 both indicator bars were much slimmer, and had a little bit of rounding to them.
This isn't much in terms of functional changes, but it might make it easier for some users to interact with the fast scroll bars which seems like it could have been part of Google's reasoning for adjusting things a little. In addition to the fast scroll bars, Google has added other adjustments in the latest version of Lollipop as well, like HD Voice, and Device Protection for compatible devices, as well as some changes to the lockscreen. Users are also starting to see the new smart lock mode appear on their devices called On Body Detection, although that doesn't appear to be specific to just Android 5.1. As more changes appear, we'll be sure to update you on what to expect when your device gets the latest Android 5.1 software down the line.