How can I fix inconsistent sleep tracking on my Apple Watch?

I have been using my Apple Watch to try and track how much sleep I’m getting (have a young baby so not getting a lot). I have only tracked two nights so far. Some nights/parts of the night it breaks down the type of sleep but sometimes not. Does anyone know why this is? What does the graded multicolour mean?

[Edited by Moderator]

Original Title: Sleep data sometimes not broken down, showing all one colour or a mix of colours.