Are you adjusting your x/y with the centre of the colour wheel , remembering that the canvas top left = 0/0
You should also bear in mind, that with a canvas of 200x200 for your colour wheel, the maximum numbers of colours it can return is 40,000. In reality this will be much less, say @ 3000. This is a far reach from the possible 16.7 million colours you can generate from an RGB value. You will only get a max of 0.24% of colours addressable by RGB. Think on 