Anthony I think I found a version of the paint mixing tool that you mention which doesn’t require downloading. I haven’t used it but I like the way that you can select the pallete that you actually have so they don’t give you a recipe that you can’t make.
Great resource! This website allows you to match a color from your reference photo and it offers suggested paint mixes from your watercolor palette. It’s free. It also has custom watercolor charts.
Super awesome, Jeff!!! Thank you for sharing this here~~~~ 