How do I change the background colour in apps

[vonnieB]

Hi all, does anybody know how to change the background colour in apps? It seems to be black and I'd like it to be white as it was..please help! 

[arvids]

On  whatsapp  go to settings,  chats, display,  shows  theme  black or white

[vonnieB]

Thankyou this is what I got. I changed it to light and tried system default, and neither changed. It's not just what's app it's all apps

[Fiona26]

Do you have dark mode turned on? Pull down your quick panel and look for dark mode icon, change it to light mode. Not sure if I'm understanding you correctly with your issue. But going by your images, your background is white.