Hey there,
To make part of the collision with other objects easier for myself to implement, I changed the floorblock.image_blend to object_index, and now able to select objects instead of blended colour values which I did not know how to properly adjust for or find (also easier for sprite work and adding in new objects etc).

You mention that this engine is well optimised in the way you have set it up, what impact would something like this then have from your original method? currently I'm not seeing an issue and hoping I won't further down the line.