Apple normally doesn't allow customizing anything in the user interface of any of its software. But there are always ways to change colors and fonts if you really wanted to.
CarPlay is no different. In fact, Apple forces developers to use a fixed interface for their apps. The layout, buttons, colors, fonts etc. are the same for all third-party apps.
So how do you change things (at least a few of them) within CarPlay? You will need a jailbroken iPhone to begin with.
My iPhone 6 is jailbroken using the untethered TaiG jailbreak which is currently available for iOS 8.1.2. Once you have a successfully jailbroken iPhone that is capable of doing CarPlay, you can customize a few things.
Change Icon Colors
If you take a look at the screenshot above from my Pioneer AppRadio 4 (SPH-DA120), I have customized the color of my 'Messages' app (Yellow instead of the default Green). This is done using Winterboard and Messages Colors Icons tweaks from Cydia.
You can also change the system default font in CarPlay by using a tweak called BytaFont 2. BytaFont is a popular jailbreak tweak that has been available for a while now. The BytaFont 2 version is compatible with iOS 7 and iOS 8.
|System font in iOS 8.1.2 has been changed|
The font I'm currently using is 'Bubblegum Sans.' BytaFont 2 has a full range of fonts you can choose from. Interestingly, some third-party apps continue using the default font on the iPhone even though the systemwide font has been changed.
|Font within the Spotify app on the iPhone doesn't change|
You can apply themes to your iOS springboard and the changes will show up in CarPlay. The fonts and app icons can be changed this way. The CarPlay interface (layout) doesn't change though.
This is what CarPlay looks like with the Lasso theme ($2.99 on the Cydia Store) applied through Winterboard...
Remove Icon Labels
You can get rid of all icon labels in CarPlay and your iPhone by using the tweak NoIconLabels. Here's a screenshot...
CarPlay customization is still in its infancy through jailbreaking. So far you can only change fonts, colors, labels and themes in CarPlay while the general layout of the interface remains the same. Maybe developers can find a way to tweak the layout like allowing more icons on the homescreen or even third-party widgets.
Have you jailbroken your iPhone and played around with some customizations? Let us know and send me some screenshots of CarPlay if you'd like to share them.
Note: Changing the system font in iOS will change the font in Pioneer AppRadio Mode interface also.