I need some help identifying this anomaly.
Newer (within 5yrs) insulated windows have staining or what appears to be a mold like substance. This was found in one upstairs window, and two 1st floor windows. The stain was on the inside of the exterior glass.
There was no stain behind the muntins, viewed from the inside. No condensation noted. Outside temp = 35F / inside temp = 62F. Water boiler heat.