Step 15: Add the other color separation shapes within the lines you just created. The first shape is similar to a big deformed oval. Place it to the left of the fish's eye, above the pectoral fin. The other color separation shape is a triangle on the blue tang's tail. The triangle should follow the same basic path of the tail. This triangle basically consists of two diagonal lines that come to a point on the right side at the base of the tail.
Step 16: For a cleaner look, erase as much as you can of the initial guide lines. Don't worry about erasing all of the guides. It's okay to leave some behind. You can also LIGHTLY erase some of the final lines so that the colors don't get too muddled with the graphite in the next step. If you accidentally erase too much of the final lines, be sure to re-draw them.
Final Step: Regal blue tangs are colorful fish, so instead of the usual shading, try coloring your drawing. Use black for the big shape inside the body. Don't color the triangle on the tail or the oval-like shape in the body. Add a bit of black on the edge of the dorsal fin on top and on the edge of the anal fin at the bottom. Use black on the pupil and a bit inside the eye on the ring around the pupil. Continue adding black to the entire section. Start adding the color lightly but eventually push down hard with your pencil to get a rich black.
Use dark blue lightly near the bottom of the blue tang's body and a bit on the middle. Color the gills dark blue too. Add some stripes on the dorsal, anal and pelvic fins using dark blue as well. Now use regular blue on the rest of the body except for the tail and the left edge of the pectoral fin. Leave a few small circles blank between the eye and the mouth, as these will be yellow spots.
Continue layering the blue, pushing harder each time until you eventually have a rich color. Use some yellow-orange to create stripes on the fish's tail and use some on the pectoral fin and spots on the face too. Now use regular yellow on everything else that's not already blue or black, including a bit around the eye. It's always a good idea to use reference as you draw. And don't forget to pause the video to draw at your own pace.