Flat design usually features large sans-serif typefaces used for messaging and titles. These bits of text look great over photos and flat colors, but as with everyone, you always have to make sure that your typography is readable. In the case of flat, where you're not supposed to use drop shadows or gradients, you have to be extra careful about readability. For this, always look to achieve the best contrast between text and background.
Let's do a quick exercise using the following steps to try out the best ways to achieve good readability:
Create a new document on Photoshop, where we will try the colors. We just want to overlay text on top of blocks, so create a small rectangle of size 160 x 175 px. Set the color of this shape as black, and create a text field inside of it in white. This contrast, white on top of black, is extremely readable. The best contrast for readability is, of course, black on top of white, like every book and every newspaper. We just created the inverse...