Thank you
all for your advice. I have now realised that they are flags. Have tried a proprietary patio cleaner with limited success. And will continue. Failing that I will turn them over. It is great to have advice from people who know what they are talking about. Thanks.
An oven cleaning chemical, Oven Pride was accidentally spilled on my coloured pressed concrete patio and has bleached it's colour. I would appreciate any advice on how to repair the damage.