Kevin Mah

I was looking for this exact bit of information. I'm sure you have your answer by now, but I thought I'd share if anyone else tries to google looking for it. From https://www.sidefx.com/docs/houdini/ref/panes/scenegraphdetails.html:

Grey
Not set
Value is not set.

Orange
Fallback
Default values provided by the schema where no value was explicitly set.

Blue
Set
Attribute/primvar value (without time samples).

Green
Time sampled
Animated value (read from time samples).

Violet
Value clip
Time sampled value from a value clip.

Indigo
Computed
Read-only intrinsic or computed values.

Red
Relationships
Pointer to another prim with some relationship to the selected prim(s).