Typing app messages in night mode

[Automat-2015]

Hello,

When I am typing a text to post on apps while in night mode,  the background turns to bright white and back to night mode when I send the message. 

I use the standard Xperia keyboard, though I am not sure if this is a keyboard or an app-Xperia issue. 

Does anybody know if there is a way to keep the night mode gray all throughout? 

[Qatrium]

@Automat

What are your phone model and android version?

[Automat-2015]

It's a Z3c (D5803) and OS Marshmallow (6.0.1)