Point (general) setting.
Input (accessibility).
Find (reverse color) and click Close.
Apple's default font is this. Heiti SC (bold-Jane, bold-Jane's English name is Heiti SC. Heiti stands for bold pinyin, SC stands for simplified Chinese, which is a simplified Chinese font included in Mac OS X Snow Leopard (version 10.6) and the default simplified Chinese font for iPhone OS 3.0 (renamed iOS after version 4.0) and iPod nano since the fifth generation.
If it can't be solved, it is the problem of the mobile phone itself. Please go to Apple for after-sales maintenance.