Interestingly, this doesn't work if you pass the inputs as an object instead of an array (e.g. {r:...,g:...,b:...}). In that case, to fix it, inside the template instead of ${inputs}, you can use ${Object.values(inputs)}. P.S. Anyone else wish you could use markdown in the comments?

Good point, thanks. I added an example with Object.values below; I have more examples in https://observablehq.com/@tophtucker/horizontal-inputs. As for markdown in comments, you could add an issue to our feedback repository; I know other people want it too, but we don't have an issue for it yet: https://github.com/observablehq/feedback/issues/new