Silica Gel Blue semi-transparent glassy substance containing an indicator as “Cobalt Chloride” a heavy metal salt. When free from moisture the Granules or beads are dark blue in color. … It indicates that the gel needs to be replaced or regenerated.This is mainly used in absorbing moisture from gas and air. Silica gel blue is an option for controlling moisture which contains cobalt chloride in it. When silica gel absorbs moisture, its beads color change from blue to purple to pink, this indicates that the gel needs to be replaced or regenerated.