Observation number one: the character is half fish. I would have thought that the colour of the skin of the top half should be pretty much irrelevant when the skin of the bottom half is scales.
Observation number two: this is just loud mouthed people on Twitter. It's as if a reporter went into a pub, heard a shouty loud man mouthing off about the blacks and decided this was a story worth reporting. There are 330 million active Twitter users. If only 0.1% of them decided to make a fuss over skin colour, that would be 330,000 racist tweets. This is a non story.