The "iron ready light" automatically turns blue or white to indicate the temperature/steam state of the iron required based on what fabric is ironed.
The iron ready light automatically turns blue to indicate that the iron is in the optimal state for certain fabrics like silk and polyester, as shown in the left side of the image below.When the iron ready light turns white, as shown in the right side of the image below, the iron is providing higher temperature/steam for other type of fabrics, for example, cotton, linen and denim.
In both cases mentioned above, this shows that the ActiveSense technology working, and this is normal.