They have to make them pretty looking, otherwise people might realize they're just paper. Nobody has the power to imbue value into a paper note, if it's not redeemable for anything of value... it's TRADABLE as long as everyone goes along and says "trade that paper to me for what I can offer you". What happens when people stop going along? There is no fallback redemption option (like gold or silver) it will literally be worth the paper it's printed on, once people no longer accept the paper because the gig is up.

The only reason FIAT notes are worth what it says it's worth, is because COUNTER-FIAT notes will land you in jail. Only certain people can add zeros to their paper...

!COFFEE