This may be caused by the following reasons:

1. Accidentally changed htop display settings

2. Terminal color scheme or theme issues

3. Font or display scaling settings in the terminal

Solutions to try:

1. Press F2 in htop to access settings menu and check display options

2. Exit htop with F10 and restart it

3. Check your terminal's color configuration

4. If using remote connections (like putty or VSCode), you might need to adjust terminal color settings