Some of the Jira drop down customfields like version picker, linked issues provide a dark background (grey) when presenting values for selection while other Jira customfields (system fields) are presented with light background. (screenshots attached).

So the behaviour is not consistent when it comes to different fields appearance, this needs to be streamlined for better user experience. Appearance of the backgrounds in different browsers is different but pattern (dark background) remains same.

Even making changes to look and feel settings doesn't help with these customfields to ensure consistency. Tried with chromium based browsers and firefox.

However, there is no loss of functionality when selecting the values, this is a request to improve UI experience for the users.