In the previous phase, you should have designed the IA and layout for the primary screens of your User Flows. Now its time to re-use those patterns and do the same thing for all the screens in your app.
You should design the layouts in grayscale and go back to the primary screens to update the layout and IA as you see the need for it now that you're fleshing out the design across different user goals.
Low Fidelity or Low-Fi is a really basic version of wireframing. It should be black and white and it's where you get scribbles for text and colored rectangles for images.
This should primarily be used when you're initially designing a screen. The more iterations you do, the better it will be, but to make sure it works in the real world, you'll want to do a few iteration passes with Mid-Fi wires.
Mid-Fidelity wireframing will be full grayscale, your buttons and cards and images can start getting some rounded corners as necessary, and you can even add shadows and borders to help create depth. RaNolan primarily wireframes in mid-fidelity.
