Many modern applications are using visual representations of data. That has potential to be helpful to the users, allowing them to better spot trends and variations in large data sets. However, the in-house applications I see are mostly using color wrong.
There is a science behind good data visualization, and commercial web-based applications have studied this. That’s why their visualizations look good and help the user. For an example, look at the flight search at www.hipmunk.com.
Unfortunately, most applications are built for in-house use and don’t have the benefit of a data visualization professional. The typical developer will simply place a default graph on a page and be done with it. It might look like this.
Image from http://blog.fusioncharts.com/2013/06/bar-charts-or-column-charts/
The color in this graph is superfluous and does not add any value; each data point is placed above its label, so there is no confusion possible. It places a cognitive load on the user, and it actually takes longer to read a gaudy bar diagram like this.
If you have a threshold value, you might decide to show all bars in neutral blue, but mark the salespeople seriously behind quota in red. But by simply ordering the values from high to low (instead of alphabetically by salesperson name), you are already giving the user enough information.
Don’t use color unless it has a meaning.