If the pattern appears to change because of the sun hitting the glass, then you probably have condensation between the panes of glass that is able to move once the sun hits it. Having condensation would mean that you have a leak or leaks in the seal somewhere.
To make sure that what is happening for the glass to appear not clean in some way, I would suggest going over both of the sides that you can reach with lacquer thinner using a very clean rag and then another very clean rag to do the drying. White paper towels without any color at all on them could also be used for the drying.
Please be sure to have adequate ventilation and wear protective gloves if you decide to try the lacquer thinner.
Did you have the window installed or did it come that way with the home, please?
