Is this home electricity supply panel ready for a current-sensing energy monitor?
You're right on the money

Yes, you have indeed found your main fuse in that clear plastic fuseholder.    I wouldn't make any guesses about the wire colors, but that's OK, because either side will work for clamping the CT onto it.  If you want to double check, simply detach the fuse-section from the fuseholder -- that should kill all power to the house if our theory here is correct.