Currently, VisualStudio2012DarkTheme has a white background in order to be able to read the labels. This change was done when addressing this item:

https://feedback.telerik.com/winforms/1535458-radchartview-the-axis-label-are-difficult-to-read-in-visualstudio2012darktheme 

However, it is inconsistent a dark theme to have a white background color. The design should be improved to achieve consistent look and feel.