(This is not a CSS question; this is a visual design / user interaction question.)
I plan to tint the alt rows to make them distinguishable:
The problem comes when expanding/collapsing nested rows. As they expand and collapse, like-tinted rows will be adjacent (eg. 1.1 and 1.2 are adjacent and both blue; potentially - 1. and 2. can be adjacent and will both be grey):
But if I adhere to a fixed even/odd row colour, like this:
that means that a given row does not maintain a fixed colour (1.2 was blue, now grey; 2. was grey, now blue):
So, as the table is expanded and contracted, many rows are changing tint. Is this visually confusing for the user? Is there a better/best answer for this setup?