As an aside - you'll notice that I flip back and forth between color and colour. I'm Canadian, so I'll respect American spelling in a title, but otherwise, it's Canadian all the way, I like the letter "u." :)
So at the Praying in Color website there are resources and examples, but the basic idea is simply doodling your prayers. You don't have to be an artist, for which I'm very grateful. You just need to be able to make shapes and lines or whatever. And while I like to pray in colour using tons of different coloured markers, you can just use a black pen or a pencil if that's what you want. I love the freedom of the practice, and in particular I love that it is not word - based (though you can incorporate words if you want). Sometimes there simply are no words and I find it necessary to have other ways to pour my heart out before God.
Occasionally I meet people who wonder how doodling can be prayer and I think it's all about intention. If you intend to enter into the presence of God, then the practice you are entering into can become prayerful. That's why I tend to start children off with this practice by having them write a name for God and doodle around the name for awhile (one of MacBeth's suggestions for kids). It focuses our attention, it helps us claim what we're doing as prayer.
Sometimes I need more structure than what praying in colour offers, and so I find colouring Mandalas to be helpful (I find this website gives some good instruction). Some refer to Mandalas as sacred circles.
To the Tibetan monks, the sand mandala represents multi-dimensional fields of spiritual consciousness and the state of enlightenment. To the Native Americans, the medicine wheel, a form of mandala, symbolizes sacred ceremonial space and the circle of life. In both eastern and western cultures, the mandala has come to symbolize harmony, unity, wholeness, and healing.Steven Vrancken
For some reason my scanner only wanted to capture 1/4 of my circle!
Other folks I know like Zentangle (which you can feel free to Google if you wish). I haven't really explored Zentangle, but from what I understand, it can be as simple or as complex as you wish. For many this is a spiritual practice, however, I'm not familiar with its origins.
Again, what I love the most about this form of communion with God, is that it does not require me to articulate in words. While I love words, and I use them a good deal in my writing, preaching and teaching, there are times when they simply fall short, and other forms of expression are needed. I look forward to creating space for this practice in the coming month.