I’ve had a few cases recently where we had to figure out why certain nodes were red in an ICE tree. Usually this was in cases where someone was building something from scratch, or using factory ICE nodes in a slightly non-standard way.
For example, here’s an ICE tree with the Emit Splash from Surface Collision and Move Towards Goal compound.
Red means the evaluation of the compound is returning an error. You can see the first of the errors that are bubbling up if you point to an empty area on a compound. To see all the warnings and errors, right-click the node and click Show Messages.
In this case, the problem is that an attribute is not initialized. Some factory default compounds rely on other compounds (usually the emitters) to initialize certain attributes. When you start building up things from scratch, you’ll have to take care of the initialization.