+printf "\033[%s" "$blue_grep" >check-grep
+if (grep "$blue_grep" <check-grep | grep "$blue_grep") >/dev/null 2>&1
+then
+ grep_a=grep
+elif (grep -a "$blue_grep" <check-grep | grep -a "$blue_grep") >/dev/null 2>&1
+then
+ grep_a='grep -a'
+else
+ grep_a=grep ;# expected to fail...
+fi
+rm -f check-grep
+
+prepare_output () {
+ git diff --color >output
+ $grep_a "$blue_grep" output >error
+ $grep_a -v "$blue_grep" output >normal
+}
+