This air contains moisture and hence the proper working of the transformer can get affected because this humidity can change the dielectric strength of the oil. So use of silica gel blue comes in handy for proper functioning of the transformer.
Silica gel blue is available in beads or granules form and is of light pink color when fully absorbs moisture while as silica gel orange beads are also use for effective moisture drying in breather transformer applications when it free from moisture then its color change to dark green. When it comes in contact of moisture its color gradually changes from dark blue to light blue and then finally pink and hence indicates the absorption of moisture. This change in color of silica gel blue indicates and alerts the user that it needs to be replaced or regenerated. It is basically used in the breathing process of Transformer.