What
wog says about not having
shades or
tints on a colour wheel is not quite true. Sometimes a colour wheel is a
filled wheel, not just a rim.
The usual technique is to have white at the centre, fading through progressively stronger tints until you reach a totally saturated colour, then moving through darker shades as you reach the black rim.
However, this does not show all colours, as colour is three dimensional: the saturation (difference of the colour from an equally bright shade of grey) is always 100% on this wheel. Also, all points on the outside are the same colour: #000000, or black.
The correct colour-shape should (I think) be a sphere: white at the top, saturated at the equator, and black at the bottom. Running from pole to pole is a monochrome bar, and running from the core of the sphere to the outside growing more and more vivid.
Or, it could be visualised as a cube of dimensions RGB. Or of hue-saturation-luminance. Or in many other shapes.
Of course, octarine is the the 4th dimension, into a hyper-cube or -sphere... of which the colours we see around us are only pale reflections of octarine-colours. But this analogy could also be used to describe alpha: how transparent a colour is. But transparency is not the same for all colours... and there are colours outside of our sight (like UV and IR that don't fit into a nice colour wheel.