Comments!
My advice would be to add comments to the code. Comments shouldn't repeat the code, but e.g. describe what it's doing, or provide links to where the formulas come from and what they mean. It's also helpful to document overall code structure (where do I go to find something?).
Formatting!
And to run it through code quality tools. A lot of minor styling issues. It could use more new lines (esp. between functions).
These sorts of things might seem minor, but they matter if you're applying for a job. A lot of people will give a cursory glance at your code repos to see if everything looks reasonable or if there's anything insane. These sorts of surface features make a disproportionate difference.
Plus, they really do help. A lot of your users might not know what LAB colors are, or how exactly HSV is computed.