"Deviation Chart and its interpretation."

I have a dataset on which K-means clustering is applied. I am trying to see through various visulaizations available if the value of K is justifiable, i.e. looking for non-overlapping clusters. One of the charts that explains it well is parallel chart, but the problem with the chart is that I cannot zoom-in to analyze closely if there is a overlap.

I also found deviation chart, which shows a line for each cluster that represents average of data points for every value of x in that cluster. But, apart from this, there is a shaded region around every line of each cluster. I am unable to understand what this shaded region represents. Can someone please explain this and significance of this chart.Please find attached snapshot for reference. Thanks