Mohammad Mattar is just one of at least 100 people who died in protests in Sudan last week.He was 26 and had travelled to the capital, Khartoum, from London.His death has led to people changing their profile pictures on social media to various shades of blue, in a show of solidarity with pro-democracy protesters in Sudan.Blue is said to be his favourite colour.His friends started the trend as a way of coping with their grief.