NX : Sketch line turns blue after doing Mirror curve operation | NX Sketch Constraints - Color Meaning

In NX Sketching mode, by default the sketch lines will be green in color.

Once you select any dimension tool to mark the dimensions of the sketch, then you may notice that the sketch lines may appear in three different colors.

Yellow - Indicates that the sketch curve is partially constrained or not constrained. (Not recommended)
Blue - Indicates that the sketch curve is fully constrained. (Recommended)
Grey with Brown dimensions - Indicates the the sketch is over constrained. (Not recommended)

So, Incase if the sketch curve turns into blue color after mirror operation, then it means the sketch you have drawin is fully constrained. It is the best practice in the industry 
to sketch the constrain fully.

Fully Constrained Sketch in NX
Partially constrianed sketch in NX

The first picture shown above is fully constrained after mirroring. But once I remove a dimension in the sketch , some curves turns into yellow (second image) that means they need to be constrained properly.