The rules for using colors in flat are pretty simple: avoid gradients and textures. These colors should be used as they are, without any modifications. Even a flat color will look like it has a bit of a gradient to it because of the way the LCD screens are built. This is because the color won't be exactly the same in every area of the screen, and also, the light that surrounds your device has some influence on it. So, try to test your colors and choose a palette that works and looks good.

There are some types of preferred colors to be used in flat though. The website, http://flatuicolors.com, is great to check these quickly as well as use them. By just clicking on the color on the screen, the hexadecimal code will be copied to your clipboard and be ready to be pasted in your Photoshop or CSS code. The colors shown on the website easily represent the kind of colors used. It's an interesting take on using vivid colors, but they should be toned down a bit. A strong and greener turquoise...