Update

By the way, it is not required to create a new coordinate list for all graphics primitives. This was only done to make the code verbose enough. The color disk, the radial lines and the circles can all be created easily using the same underlying data. Here the Span operator (;;) becomes handy, to achieve high resolution in the color disk, but have only some radial grid lines.

With[{pts = Append[#, First[#]] &@ Table[{r {Cos[phi], Sin[phi]}, phi/(2 Pi)}, {phi, 0, 2 Pi, .1}, {r, 0, 1, .1}]}, Graphics[{Polygon[{{0, 0}, First[#1], First[#2]}, VertexColors -> (Hue /@ {{0, 0, 1}, Last[#1], Last[#2]})] & @@@ Partition[pts[[All, -1, {1, 2}]], 2, 1], Black, Opacity[.5], Line[pts[[;; ;; 3, All, 1]]], Line[Transpose[pts[[All, All, 1]]]], Opacity[.2], {Line[#], Line[Map[Reverse, #, {2}]]} &@ Table[{{x, #}, {x, -#}} &@Sqrt[1 - x^2], {x, -1, 1, .1}] }]] 

It is of course possible to draw everything manually.

Manipulate[ With[{ colArea = Polygon[#2, VertexColors -> ConstantArray[Hue[#1/(2 Pi)], 3]] & @@@ Table[{phi, {{0, 0}, {Cos[phi], Sin[phi]}, {Cos[phi + Pi/40], Sin[phi + Pi/40]}}},  {phi, 0.0, 2 Pi, Pi/40}], gridLines = Table[{{x, -#}, {x, #}} &[Sqrt[1 - x^2]], {x, -1, 1, 2/(grid - 1)}], radLines = Table[{{0, 0}, {Cos[phi], Sin[phi]}}, {phi, 0, 2 Pi - 2 Pi/radiants, 2 Pi/radiants}], cirLines = With[{ circle = Table[{Cos[phi], Sin[phi]}, {phi, 0, 2 Pi, Pi/20}]}, Table[r*circle, {r, 0, 1, 1/circles}] ]}, Graphics[{ colArea, Black, Thin, Line[gridLines], Line[Map[Reverse, gridLines, {2}]], Darker@Gray, Line@radLines, Line /@ cirLines}]], {circles, 3, 10, 1}, {radiants, 4, 20, 1}, {grid, 5, 20, 1} ] 

It is of course possible to draw everything manually.

Manipulate[ With[{ colArea = Polygon[#2, VertexColors -> ConstantArray[Hue[#1/(2 Pi)], 3]] & @@@ Table[{phi, {{0, 0}, {Cos[phi], Sin[phi]}, {Cos[phi + 2 Pi/colors],  Sin[phi + 2 Pi/colors]}}}, {phi, 0, 2 Pi - 2 Pi/colors, 2 Pi/colors}], gridLines = Table[{{x, -#}, {x, #}} &[Sqrt[1 - x^2]], {x, -1, 1, 2/(grid - 1)}], radLines = Table[{{0, 0}, {Cos[phi], Sin[phi]}}, {phi, 0, 2 Pi - 2 Pi/radiants, 2 Pi/radiants}], cirLines = With[{ circle = Table[{Cos[phi], Sin[phi]}, {phi, 0, 2 Pi, Pi/20}]}, Table[r*circle, {r, 0, 1, 1/circles}] ]}, Graphics[{ colArea, Black, Thin, Line[gridLines], Line[Map[Reverse, gridLines, {2}]], Darker@Gray, Line@radLines, Line /@ cirLines}]], {circles, 3, 10, 1}, {radiants, 4, 20, 1}, {grid, 5, 20, 1}, {{colors, 20}, 4, 120, 1} ]