You can customise an iPhone by adding iPhone applications to the device. Apps allow you to add functionality to your iPhone. But apps approved by Apple don't allow you to customise the font, font size and font colour on your iPhone. You can add apps that have not been approved by Apple if you jailbreak your iPhone. Numerous websites offer information on the jailbreak process. If you have jailbroken your phone, you can use the Cydia and WinterBoard apps created by Saurik to change text colours. Jailbreaking voids your warranty with Apple.
Tap the "Installer" icon on your iPhone. This opens the Installer interface. Tap the "Sources" icon at the bottom of the interface, then add "http://apptapp.saurik.com/" (without quotation marks) as a source. Tap the "Install" icon at the bottom of the interface, tap to the "System" category, then tap to install "Cydia."
Tap the "Cydia" icon on your iPhone. This opens the Cydia interface. Tap the "Search" icon at the bottom of the Cydia interface. Type "WinterBoard" (without quotations) in the search box, then tap the "Search" button. Tap to download and install WinterBoard when it is displayed in the list of results.
Tap the "Sections" icon at the bottom of the Cydia interface. Locate "Themes (Springboard)" in the Sections page and tap to install any that you like. Tap to close Cydia.
Tap the "WinterBoard" icon. This opens the WinterBoard interface. Open the "/private/var/stash/Themes.y9qoV5/Saurik/" folder and tap to edit the "Info.plist" file.
Type the colour you want for your font, replacing the word "white" in this block of text with the new colour:
Tap to save the edited file. The fonts on your iPhone will be changed to the colour you selected for the theme.
Jailbreaking your phone may lead to its becoming permanently unusable.
Jailbreaking is legal, but it voids your warranty with Apple.