Color is a great way to convey energy and communicate important information. Although, too much color at once can be overbearing and overload the visual senses. Here are some best practices for choosing when and how often to use color.
Use Complementary Colors - Choose colors that work well together. They should not distract the user from what you are trying to convey. For instance, if you want to use a few pastel colors inside of your app, its probably best to choose a coordinating set of pastels. If you want to use your church's logo and it's a specific color, make sure that it goes with the color scheme of your app - if it doesn't, consider making your logo white.
When designing your home menu, perhaps use a gradient of color over all the images so that it looks like each picture blends somewhat with each other. Use the Google Color Tool to help you find complementary colors that will go with your church's main colors.
I recently painted my house & showed my wife the colors that I was thinking on using. She very quickly taught me this thing called "Complementary Colors." Boy, was I glad she showed me how important this is.
Be Selective with Using Colors - The less color that you choose to use, the more it "Pops" when you do choose to use it. Use color judiciously for communication. For example, a big green "give" button inside of your app becomes less effective when green is used elsewhere in an app for non important reasons.
Test Your App's Color Scheme Under a Variety of Lighting Conditions - What looks good inside of your office with florescent lighting probably won't look the same inside of a coffee shop with natural lighting. Build your app, and test it out by going different places with different lighting options. For example, colors don't pop as much with natural lighting, but those same colors may look to "bright and bold" inside of your church office.
Be Aware of Color Blindness - At the last church I was at, I had a few color blind people come up to me and let me know that specific colors were hard to see for them. For instance we had a few buttons that were red and when clicked, turned green. This was too hard to distinguish for a handful of people in our church, so we changed out the colors.
Be Mindful of Color Contrast Ratios - Contrast is essential in your app to make sure that everyone can read what you put in there. The text might blend in with your background and this can make it harder for a certain group of people to read it. The industry standard is to have a minimum contrast ration of 7:1, but at minimum a ration of 5:1 is best.