Blue feather on my icon

Good morning all,

Hope you all had a descent weekend.

I have created an assembly with some components that I have placed.  I have now created another part that has just the cys and the 3 planes only.  I have assembled this new part into my other assembly so that I can create the new part's features while in the assembly.  Basically I want to be able to create the new part while in assembly mode and create it around existing part's geometry.  I have noticed in my assembly model tree my first four existing parts, their icons which were just the normal part block icon now have what looks like a blue feather across the prt icon and the new prt with just the cys and 3 planes does not.  What is the "feather thingy" and how can I toggle between individual parts and assembly level to work on each level?

Thanks guys.

Sid

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