Please get our latest package, our developer enhanced the logic of keycolor and it should works for your scenario.
You can add the color for example red into Layer.KeyColors, and it will be rendered as transparent.
Because our logic loop all pixels after you set the keycolor, if you used this API the performance will get effected.
Our development team also discussed your other thread about add multiple images into one layer, we don’t have the plan to add this feature into our map. If we want to support it which means we have to handle too many different data format in one layer, it will introduce lots of problems, and we have “Overlay” as layer container to collect different type data, for common scenario this type layer is duplication in function.
But you can implement it by write a custom layer, you know which types you need and it works for your scenario.
Wish that’s helpful.