diff --git a/colours.sh b/colours.sh
index 793faf6..6e8d583 100755
--- a/colours.sh
+++ b/colours.sh
@@ -32,3 +32,44 @@ for fgc in {30..37}; do
 	done
 	echo; echo
 done
+
+rainbowColor() {
+	local h=$(($1 / 43))
+	local f=$(($1 - 43 * h))
+	local t=$((f * 255 / 43))
+	local q=$((255 - t))
+
+	if [ $h -eq 0 ]
+	then
+		echo "255 $t 0"
+	elif [ $h -eq 1 ]
+	then
+		echo "$q 255 0"
+	elif [ $h -eq 2 ]
+	then
+		echo "0 255 $t"
+	elif [ $h -eq 3 ]
+	then
+		echo "0 $q 255"
+	elif [ $h -eq 4 ]
+	then
+		echo "$t 0 255"
+	elif [ $h -eq 5 ]
+	then
+		echo "255 0 $q"
+	else
+		# execution should never reach here
+		echo '0 0 0'
+	fi
+}
+
+rf(){ echo "$1" 0 0; }; gf(){ echo 0 "$1" 0; }; bf(){ echo 0 0 "$1"; }
+for f in rf gf bf rainbowColor; do
+	for s in "$(seq 0 127)" "$(seq 255 -1 128)"; do
+		for i in $s; do
+			# shellcheck disable=2183,2046
+			printf '\x1b[48;2;%s;%s;%sm ' $($f "$i")
+		done
+		echo -en "\x1b[0m\n"
+	done
+done