I have a long list (1000+) of hex colors broken up in general color categories (Red, Orange, Blue, etc). When I show the list of colors in each category I need to show them in order of shade. i.e. light red first and dark red last.
What would the algorithm be to do this? (googling has failed me)
It sounds like you want to sort them by intensity. Try searching for that.
Convert the colors from RGB to a HSV or HSL scale and then sort them by Value or Lightness. Lightness might work better as it would capture the "faded" colors better, such as pink->red->dark red.
If you convert the colors to HSV space, you could potentially sort them by the hue, then the value.
The hue will determine the color "category" - ie: red, blue, green, etc.
The value and saturation will affect the "lightness" of the final color. You might need some experimentation to get the ideal sort, though.