I took a look at Amelia’s CodePens and can’t find the solution I am looking for
I think you’ve overlooked the pens with the feColorMatrix https://codepen.io/AmeliaBR/pen/WvwwME
The matrix is a bit daunting (not something I plan on delving into myself) but you can use this handy online generator to work out the values https://codepen.io/jacobberglund/pen/ORNQAr
There’s also this generator, which is even easier http://blog.andresgalante.com/RGBAtoFeColorMatrix/
In both cases, just slide the bars until you achieve the effect you’re after.