Ok, I see, easy fix and I passed. Thanks.

That doesn't seem to be the issue, as the error appears for n = 254: for n = 254, at index 232, expected: "#e9e9e9" but got: ""
the index where it doesn't find any entry seems to change everytime I run it, attempting again, I get for n = 254, at index 193, expected: "#c2c2c2" but got: "".

Thanks for this, the comments are nice xxx

If you program recursively, the intermediate fractions need to be stored in memory. But this probably only takes up a little more space on the stack until the function finally returns, so even with millions of calls it doesn't really matter.