Use Edit Object Display to change the part colors in an assembly when you follow the steps in this tutorial from user @Ganesh_Kadole. Thanks for sharing, Ganesh!
When you change the color of a component within an assembly by 'Edit Object Display', either by selecting the component in the UI or making it as work part, you are actually changing the color of the component in the context of the main assembly.
Before changing the color of the component, under the properties of the component check option 'Specific Component Color'. It will be grayed out. See the example below.
Now, if I change the color by selecting the component or making it as work part. The option 'Specific Component Color' will become active and it can be unchecked at any time.
Start the command 'Edit Object Display' (Ctrl+J)
From Filters, set the Type filter to 'Solid Body' > Select the component > Change the color > Under Settings of the 'Edit Object Display' window, check the options 'Apply to All Faces of Selected Body' and 'Apply Changes to Owning Part' > OK.
With these options, color of the component will change at assembly level as well as at part level.
Please Note: If you start the 'Edit Object Display' command and do not set the filter, you will not be able to select the options 'Apply to All Faces of Selected Body' and 'Apply Changes to Owning Part'.
Assign Feature Color will change the color of the faces which are created by that particular feature only.
Here I have used 'Assign Feature Color' on the edge blend feature. Note how this changes the color of blend faces only, not the faces of earlier feature.