<p>This paper seems to have quite a discussion: 
<a href="http://arxiv.org/abs/1109.2323" rel="noreferrer">An inventory of three-dimensional Hilbert space-filling curves</a>.</p>

<p>Quoting from the abstract:</p>

<blockquote>
  <p>Hilbert's two-dimensional space-filling curve is appreciated for its
  good locality properties for many applications. However, it is not
  clear what is the best way to generalize this curve to filling
  higher-dimensional spaces. We argue that the properties that make
  Hilbert's curve unique in two dimensions, are shared by 10694807
  structurally different space-filling curves in three dimensions.</p>
</blockquote>
Algorithm for generating a 3D Hilbert space-filling curve in Python
<p>I'd like to map points in a RGB color cube to a one-dimensional list in Python, in a way that makes the list of colors look nice and continuous.</p>

<p>I believe using a 3D Hilbert space-filling curve would be a good way to do this, but I've searched and haven't found very helpful resources for this problem. Wikipedia in particular only provides example code for generating 2D curves.</p>