I don't think they were doing EVAs or anything, so I don't really know how impressive the boots need to be, although I am thinking the construction boots / loggers on the middle two are not the regulation ones.
I am picturing them realizing they didn't bring their boots or they were still being made on picture day, so NASA engineers running around trying to find people who had a pair of boots they were willing to let them spray paint LOL.
Looks like left and right are wearing the actual boots btw
https://airandspace.si.edu/collection-objects/boot-left-mercury-schirra/nasm_A19721158005