The act and art of coloring, once reserved for children, is now being seen as a form of therapy for adults, and adult coloring books have become increasingly popular. There are a few great places online to download pictures to print and color by hand, and there are also some terrific apps for the sizable iPad screen.

But where can you color on your iPhone? Whether you commute to work via public transportation or just want to relax on a break or at lunchtime, these adult coloring apps for iPhone can help you relax and unwind.

1. Recolor

Recolor provides a good number of images to work on. It's a tap-to-fill coloring app with a zoom feature to color even the tiniest details. From animals and flowers to 3D and folk art, there's something for everyone here. Free content is added daily, so you will always see a new image to spark your creativity.

There are more than 10 color palettes included, and you can select different shades of colors with a simple swipe from the bottom of the screen. When your masterpiece is complete, you can save it to your device. You can also share it from within the app to social media or send it via text or email. One standout feature of this app is that you can scan in your own images to color or open one from your library.

Recolor is available as a free trial for seven days, and you can subscribe at a yearly rate if you really enjoy the app and find yourself using it a lot. Recolor is also available for iPad.

If you have an Android device, try these best coloring book apps for adults on Android instead.

Download: Recolor (Free, subscription available)

2. Color Therapy

Color Therapy is another tap-to-fill app and also has a lovely set of images. From places, people, and patterns to Mardi Gras, Chinese New Year, and mandalas, the selection is extensive. There are countless color palettes between solid shades and gradients. You begin with a couple of basic palettes but can unlock others easily with a VIP All Access subscription.

What makes Color Therapy stand out, aside from the background music selection, are the effects you can apply to your finished pictures. You can add a simple frame and choose from watercolor, woodgrain, or fabric filters. You can then share your creation directly from the app to social media, text, email, or just save it to your device.

Color Therapy is available for free with plenty of images to pick from. You can obtain additional color packs, frames, songs, and remove the adverts via subscription. Color Therapy is also available for iPad.

If you are seeking a coloring book to please your child, try these children's coloring apps for the iPad and iPhone.

Download: Color Therapy (Free, subscription available)

3. Pigment

If you prefer a "true" coloring experience, rather than the tap-to-fill options, then Pigment is for you. You can choose from different tool styles, such as the pencil, marker, or airbrush. You can also adjust the opacity and size of each tool.

Pigment offers a large image library with geometric designs, organic patterns, and 3D structures, as well as the basics like butterflies and animals. The app has over fifty total color palettes, at least half of which are free, and it lets you adjust the shading for each color you choose, which is a great option.

Like the other apps, Pigment lets you share your creations via social media, text, or email. There is an active community within the app, so you can view other people's finished creations and use them to inspire your own work.

Pigment is available for free, but you can sign up for a subscription to access all of its coloring books as well as more color options and tools. Subscribing removes the Pigment watermark from your pictures and lets you save them in high resolution. Pigment is also available for iPad.

Download: Pigment (Free, subscription available)

4. Adult Coloring Book

Adult Coloring Book offers many highly-detailed images to really sink your creativity into. You can choose from polygons and pixels to gothic and geometric shapes. The app provides a little inspiration with its pictures as well—just tap to Get Inspired under any of the images to check out those shared to the Instagram Hall of Fame.

You start out with a very basic color palette and can unlock a couple of others by sharing your artwork. Zoom in to better reach the details and hit the Undo button if you change your mind or make a mistake. Adult Coloring Book provides common sharing options and even lets you sign your picture before you share it.

Adult Coloring Book has a few other features worth noting. You can select a relaxing ambience while coloring and choose from options like songbirds, a babbling brook, or the seaside. You can also apply a texture to your picture while you are coloring (or when you are finished). From brick to silk to watercolor, these help to give your artwork a special look. Another notable feature is the animation option — just tap to see an animated version showing how you colored your wonderful masterpiece.

Adult Coloring Book is available for free with a premium subscription that unlocks all books and palettes. Adult Coloring Book is also available for iPad.

Download: Adult Coloring Book (Free, subscription available)

5. Colorfy

For something a little different, Colorfy has many image options with a few unique ones like Zodiac, gardens, cats, and special dates. Similar to Recolor, this app lets you pull in an image to color from your device's photo library.

Colorfy offers a basic color palette along with a free daily palette to get you started, and you can easily create your own color combinations. Like Adult Coloring Book, you can get some inspiration from other users who have shared their pictures.

The filters available with this app are what make it stand out. You can choose to remove the lines from your artwork completely. Then apply a neat effect such as pop art, neon, or bokeh for an extra unique look. Or adopt an art style for your image such as Expressionism, Surrealism, or Cubism.

Colorfy is available for free with many wonderful options. A premium subscription unlocks all features and provide new images every day.

Download: Colorfy (Free, subscription available)

6. Lake

Lake is a unique cross between a coloring book and a journal. The focus is on relaxing through creativity, with a color palette suggested for you to suit your mood and pieces of artwork offered to match your preferences. All of the illustrations are created by indie artists who receive a portion of every subscription fee, so you are supporting working artists through this app.

The interface is simple and uncluttered, and the tools are simple to use. You can click to color inside the lines, or choose to go freestyle. The Apple Pencil is supported on iPad, and all of the expected sharing options are available.

What sets Lake apart, aside from the wonderful design that won it an Apple Design award, is the ability to insert your finished pieces into a journal and record your thoughts each day. If this aspect appeals to you, try these gratitude journaling apps to boost mental health.

Lake is free with a subscription available that provides access to over 900 extra illustrations and the full journaling experience.

Download: Lake (Free, subscription available)

Have You Jumped Onto the Adult Coloring Bandwagon?

This activity for adults is said to help reduce stress, improve focus, and allow us to cope better. One doctor even has a different thought on this now common form of relaxation therapy. Medical Daily quoted Dr. Joel Pearson, a brain scientist at the University of New South Wales in Australia, who presented a different explanation for the therapeutic effect:

Concentrating on coloring an image may facilitate the replacement of negative thoughts and images with pleasant ones... It should occupy the same parts of the brain that stops any anxiety-related mental imagery happening as well... Anything that helps you control your attention is going to help.

Whatever the psychological reason (even if just for fun), many adults seek out coloring websites and apps. Coloring can help you relax and relieve stress or just pass some time. Do you have other iPhone apps that you like for coloring? If not, all of these apps let you get started for free, so they are definitely worth a look.