Because the skirts that they wear are now so short and tight, the head teacher at the school two of my granddaughters attend has decreed that the girls must all wear black or very dark coloured knickers. Such a shame for panty perverts like me who live for sightings of colourful girls knickers and the consequent masturbation.

Doubly problematic for me is that my eldest granddaughter is now eighteen, in her final year at school, has passed her driving test, hence there is no excuse for me to go to the school to pick the girls up anymore. The upside though is that I still go across to their house to walk the dog, and I wait for the girls to arrive home for tea and a chat.

Yesterday was good. They arrived home and I was amazed that the skirt of the elder girl was so short and tight that I could clearly see her thigh gap as she walked. They both sat on the settee opposite me. The sun shone through the  window and right up their skirts. Hence even though both their knickers were regulation black I could see the satiny black triangles with complete clarity. I got so agitated that I put down my teacup, went into the downstairs toilet, and masturbated until I obtained a measure of relief as my cum dripped into the bowl. Not long afterwards their mum arrived home from work, so I took myself off home in the car. But on the way I needed to pull into a lay-by and masturbate again. The urges I have for the girls panties proving too powerful for me yet again.