Draw transparency in canvas

How can I draw transparency into canvas?

Like erasing parts of the image, the same as drawing with black or gray in the alpha channel.

Does a "no-color" color exists like the Overlay of MMF used to have that erase it?

*Note that I need to really erase the canvas texture by drawing, not just a cosmetic erase through shaders.

I think your best option is to use the erase fx. Otherwise you will be forced to constantly erase the canvas, then redraw/ re-paste into it.

On the plus side, paste preserves a sprites opacity, so it is possible the fake an alpha channel that way.

Thanks newt.

I would prefer not to use the paste sprite trick but it seems to be the only way.