Breaking it down
- Substitution
sed "/$*/Is/^\([^:]*:\) *\(.*\)$/\1\n\2\n/p"
/I - case-insensitive match \(...\) - capture ... for reference as \1 \n - a newline character
sed "/$*/Is/^\([^:]*:\) *\(.*\)$/\1\n\2\n/p"
/I - case-insensitive match \(...\) - capture ... for reference as \1 \n - a newline character