Blue Diamond is in mourning, and makes those around her sad.

Yellow is angry and her anger is contagious (Blue in the Trial, Peridot etc).

Pink Diamond is usually happy, and spreads love to those around her (even if she wasn't the greatest person).

The way I see it, White could represent one of two things: Apathy or Fear.

Apathy makes sense because it's white, it's the lack of color, the lack of emotion. Her gem is on her head, she could be purely intellectual.

However, fear also works because her design is filled with spikes, and being afraid or anxious is associated with being "in your own head".

Or... perhaps a combination of both.

My prediction for White Diamond is that she puts on a guise of being purely apathetic and intellectual while secretly being afraid on the inside. She strikes fear into the hearts (gems?) of those around her because she's secretly scared herself-- she just hides it. She's afraid of losing control, of losing power. She's afraid of gems finding out their true potential. She's afraid of getting close to anyone, which explains her absence from pretty much everything Pink-related.

Just imagine Steven meeting White Diamond and not being able to feel anything at first. His empathy powers-- his greatest strength-- would be useless.

But then, she starts to crack under pressure and...

...I understand now. You're scared.

What did you say?

You're afraid of losing power, you're afraid of not being what everyone expects you to be--

Stop being ridiculous. I am a Diamond. I don't feel--

It's okay. I'm scared too.

What's the use of feeling..?