Microsoft SwiftKey is a popular keyboard app on Android. It offers an array of configurable settings, including the size of the keyboard, if a number bar is always present at the top of the keyboard, and how auto-correction works. SwiftKey is also designed to learn predictive text suggestions from what and how you type.
One thing you can do to customize your keyboard further is to use a theme. There are hundreds of themes that you can choose from, or if none of them suit your preferences, you can go further in-depth and create your own theme from within the app.
To configure the appearance of your SwiftKey keyboard, you need to open the SwiftKey app, then tap on “Themes”.

The themes will open into the “Yours” tab by default. This tab displays a list of your downloaded themes. Here you can try them out by pressing the blue keyboard icon in the bottom-right corner of the screen. With the keyboard open you can instantly switch between your keyboard themes by tapping on them.

The “Gallery” tab is where you can scroll through pre-configured keyboard themes. If you tap one, you can see a preview screenshot of what the theme will look like when in use. If you like the appearance of the theme, then you can then press “Download” to download it. Alternatively, you can tap “Close preview” to close it and keep searching.
Tip: When you download a theme, it will be automatically applied.

If you change your mind on a theme that you have downloaded, you can delete it from the “Yours” tab by pressing and holding it, then tapping “Delete”.

Steven says
I have several different themes downloaded for my Android phone, but no matter which one I select, only the basic B&W is actually usable. My phone is refusing to use any of the other ones I downloaded. This sucks.