The yellow segment is the those who voted to leave. Look how small it is compared to the whole set of public who could, in principle have voted. (Blue is remain and the two grey bits are people who didn't register, and registered but didn't vote.) This is being taken as disproving the idea that Brexit is 'the will of the people' as worked up Brexiteers tend to blather, because it appears to be a minority decision.
Unfortunately, those who use this chart simply don't understand the statistics that arise from a voting system like ours. You could never definitely say what the will of the people is for sure unless you force everyone to vote. Look at this chart below. Here the grey section is the equivalent of the yellow section above - it's the people who voted for the actual outcome. A far smaller slice.
Terrible, isn't it? Clearly not democratic. Yet the grey section is the percentage of people voting for the government in the 2015 election.
The fact is that unless you do make it a legal requirement to vote, you have to assume that those who don't vote don't mind the outcome and can't be counted. It's the only possible sensible thing to do - and because of that, the way these pie charts are being used is manipulative and wrong. I don't mind you arguing for or against Brexit. Each has powerful arguments. But I do mind if you are going to misuse statistics.