Detail of the aft (active) side of the Gemini heatshield subjected to
reentry-type temperatures. See the NASM collection ID #A19781814000
page, which notes that this heatshield "may have been installed on Gemini 2").
In this view, it is more obvious that the inserts placed in the core sample
holes are merely similarly-colored (which are even more obvious from the opposite side).
To see what a Gemini heatshield looks like after a core has been removed, see
this photo on Gemini 12 at Adler Planetarium.