I have found a few apps that I believe work wonders for spriting and coloring if you want to try them.
On Android, I use an app called Pixel Art to try my hand at spriting. iOS doesn't have this app sadly.
On iOS, I use Color Effects to do recolors, as it automatically changes the whole picture to greyscale, you can zoom almost as far as you like, there are different brush sizes and opacity levels to slide to, and you can mix colors. There is also an "original color" option. Android has this same app, but it isn't as great.
I usually save the files to my Dropbox when I'm done so I can access them from my computer later. You may want to try out these apps.