Hi
In the absence of any discharge, pain, itchiness or swelling, this change in the color of your glans may not be something that you should be very worried about.
This may be a discoloration brought about by temperature change. Just continue to observe this. The glans is covered by a very thin skin and this makes the skin more sensitive and fragile than most parts of the body. Blood vessels lie underneath the thin skin and tightening and widening of these blood vessels as a response to temperature changes may bring about this change in color.