In the new Siemens NX versions, If you create a closed region by the curves, the inner area of the closed region color changes to light blue. You can turn off this setting. The figure shows the setting to turn off the “Shaded Region” setting.

As shown in the figure; to close the light blue shading in the closed contour area in NX sketching, Turn off the “Shaded Region” setting in the “View Ribbon Bar“.