Roof tiles discolouring under velux window

[hollieamin]

The roof tiles directly underneath my attic velux window have discoloured - they actually look as though they have been cleaned with a pressure washer - i know have a very distinctive stripe which is the same width as the velux window, all the way done to the guttering which looks very unsightly. I have no leaks in the window itself.
Does anybody have an answer for this as i am afraid that in time my tiles may be washed away!

 

[freddiemercurystwin]

Any chance of a photo, you sure the tiles under the window are the ones that have not discoloured and that all the rest have discoloured instead?

 

[hollieamin]

will try to take a photo later today and post - but no is the answer, all theother tiles are the same colour front and back and the same as neighbours, they have the usual moss growth also. The strip under the velux window looks immaculately clean so not sure if it could be that water is collecting on the windows and running down the tiles?? therefore cleaning them?

 

[freddiemercurystwin]

They do not look the same as they are not subject to the same run-off from the tiles above them.

 

[tony1851]

Could it be the run-off from the lead killing the lichen or whatever it is and making the tiles look cleaner?