When I would watch Who's The Boss I always wondered why the kitchen wall phone was a red colored wall phone because I always thought colored telephones were weird and the set designers could've gotten a regular beige colored wall phone to use for the kitchen in Who's The Boss. Was colored telephones all the rage in the 80's?
Bestie

Yeah I remember at the time a lot of people were getting colourful phones (in real life/not just on tv).

AT&T had a series of pastel ones that you'd see on TV all the time that replaced the classic black or beige model. Like on Family Ties they had a pastel yellow one that always stuck out to me. Below is an image of a popular model (which are antiques now!) and their various colour options. I remember seeing the green one a lot myself growing up!

So seeing the red one WTB wasn't odd to me at all, since almost everyone in my family were buying similar colourful phones.

So that's why Who's The Boss had a red colored wall phone? Those telephones always reminded me of the direct dial telephones motels used to have and I thought they looked cute
Bestie

Oh I don't think it was a conscious decision from the writers or producers like "hey we have to have a red phone", I assume it was just the set designer choosing red because it matched the kitchen design. A lime green or pastel yellow phone wouldn't have blended as nicely! I miss those old phones though, they were so sturdy and a real bell being rung inside (vs. a small speaker making a chirp noise)