Question about QGraphicsItem and cache mode

[tbscope]

So I guess changing the color isn't a transform?

No

Is there any way to use this cache mode and do what I want it to do? ie update the chache everytime the color changes or everytime I click on it?

Not with this cache mode, it is very specific (hence why it is fast). Use QGraphicsItem::ItemCoordinateCache or write your own cache.