The ash eruption from Poás Volcano reached 500 meters on Tuesday. In addition, this particular eruption was peculiar as it was red.
Volcanologist Guillermo Alvarado of the National Seismological Network (RSN) pointed out that
the gray color is fragmented lava… The reddish color is possibly due to very fine ash with mineral components of iron 2+, but it remains to be analyzed. The yellowish or yellow-greenish colors are by oxidation of sulfur.
On August 28th, 1993, during a pyroclastic eruption from Arenal Volcano, we saw coarse gray ashes and fine red ash.”