afni.nimh.nih.gov

Hi Adam,

To do such a thing in afni would require you to construct the
overlay dataset yourself, which is to say the direct answer to
your question is no (in the case of afni).

In suma however, you can have many overlays, and can control
the order and opacities of each of them. Consider reviewing
the class handout on suma, starting on slide 56 and focusing
on 65 through 73.

[afni.nimh.nih.gov]

- rick