Just to jump back a bit - it kinda already is an app. It's a Progressive Web App which might not mean very much now but in the next few years we'll start to see more of these pop up. It's like an app you don't need to install through the app store. That's what the "Add To Homescreen" message does, it adds it to your phone as if it were an app. Also I have no interest in making money from this, I have a job and I get money from that. You wouldn't pay money to download a PDF conversion chart right? Then I don't expect people to pay money for this thing I made which achieves basically the same goal ☺️
And with regards to adding other product lines to compare to - there are a few I intend to do but it's worth pointing out the target audience I have in mind with this. People who are buying kits with paint codes and are building up a collection with another manufacturer. So that doesn't really cover a lot of the more "specialist" ranges and paint ranges that are all about finding the exact colour paint. Conversion charts and apps like these will never find you the exact colour so I'm not even going to tread into those waters. I'd rather do a simple thing well than do a complicated thing badly! Also I'm only really looking to add product ranges that publish conversion charts - it means I don't have to rely on the colour matching algorithm entirely which, as nheather pointed out, can be a bit inaccurate sometimes. Especially when trying to compare, say, a metallic coat to a matt coat. I have some weighting built in for that but it's not perfect.