The error can be seen here: https://pasteboard.co/GzbUM7H.png
When using tints it is an "icons" property rather than "icon" and it looks like this:
{
type = "assembling-machine",
name = "plastic-forming-plant",
icons = {{icon="base/graphics/icons/chemical-plant.png", tint={r=0.5,g=0.5,b=1,a=1}}},
...
