In this case, sure. But what if we shifted to rendering with emojis or whatnot. What would the first ASCII character of the string be?

If you anticipate that need, you just store the gradient as an array of strings, and you still then only need a trivial lookup.

I was more commenting on the language design here; the idea of indexing into a UTF-8 string and returning an ASCII character. What does the index count? Bytes? There doesn't seem to be a way to get UTF-8 characters from strings?

Ed: There seems to be an UTF-8 library:

https://github.com/jordanhubbard/nanolang/tree/main/modules/...