Calisun,
I am not sure what material the builder used but it was significantly darker than rest of the cement. The patch work was so sloppy that after it was finished, the hairline crack became much more noticeable (a thick jaggered line measuring an inch wide as opposed to a hairline crack...
Same thing happened to us as well. We requested builder to fix the crack but after they patched it, it looked much worse. We ended up putting in epoxy.