Color Thief has been around for awhile and in the most recent update it has become a Universal app (runs nicely on both your iPhone and iPad). This app does one thing, but does it very well! It lets you apply the tone from one photo to any other photo. The interface even makes it fun to just swipe through your photos to see random combinations. Here is a very simple example using myself in a coffee shop and a building during sunset. The original images are in the upper right corner and the lower left corner.
When the coolish sunset was applied to my face I got a bit cooler (the lower right photo). You can see the little arrow pointing from the cool sunset downward towards my face. On the left side the warm colors from the coffee shop were applied to the sunset. The sunset then became much warmer (upper left photo).
Here is a really nice video that shows the features of the app.
Color Thief is currently on sale for just $1, which is easily worth it if you are ever trying to get a similar look to a group of photos. If you have one shot with ‘good’ tones you can get that look on all the other shots. Just like a nice preset in Lightroom (for those that use Lightroom).