Telerik® JustCode™ performs inspections over your code to find compiler errors and warnings and also code inefficiencies determined by some rules
(check Solution Wide On-the-fly Analysis to find out what inspections performs Telerik® JustCode™).
Once Telerik® JustCode™ finds an error or warning, it highlights it with a different color.
In order to get inspection details, hover over the error or the warning with your mouse (like it is shown on the screenshots).
In case you use a custom theme for your VisualStudio environment or if you want to change the default colors, navigate on the VisualStudio main menu to Tools / Options / Environment / Fonts and Colors. Search for JustCode Error Marker and JustCode Warning Marker and change the Item foreground color to whatever color you like.