Not sure what you mean by "adjustable in colour". The code below does the full colour wheel - it should give you a starting point anyway.
% Set parameters (these could be arguments to a function)
rInner = 80; % inner radius of the colour ring
rOuter = 200; % outer radius of the colour ring
ncols = 12; % number of colour segments
% Get polar coordinates of each point in the domain
[x, y] = meshgrid(-rOuter:rOuter);
[theta, rho] = cart2pol(x, y);
% Set up colour wheel in hsv space
hue = (theta + pi) / (2 * pi); % hue into range (0, 1]
hue = ceil(hue * ncols) / ncols; % quantise hue
saturation = ones(size(hue)); % full saturation
brightness = double(rho >= rInner & rho <= rOuter); % black outside ring
% Convert to rgb space for display
rgb = hsv2rgb(cat(3, hue, saturation, brightness));
% Check result
imshow(rgb);
