Quick guide on RuneLite player indicators and how to set it up to tell if someone is team when not in clan chat, but in friends chat.
Click to expand the window and press the wrench tool button and scroll down to Player Indicators and press the gear icon.
Within Player Indicators, scroll to Highlight Options and check the box that highlights other players
Here's an example of what it should look like in game:
Where 0tis is in the Friends Chat but not the Clan Chat, his name is white like xMadChild who is in the FC and CC. But the other randoms scrolled over have red names which means they're not in FC or CC. Red is personal preference, choose whatever color you want.
This should help everyone be more careful with clicks as long as you're in the Friends Chat, being invited to the Clan Chat should not matter.