As common dice, each of them has exactly 21 dots, they all have only numbers between 1 and 6, but the dots are distributed differently:

Red die: 1,1,4,5,5,5
Black die: 3,3,3,4,4,4
Green die: 2,2,2,3,6,6
Blue die: 1,1,1,6,6,6

What is special is that:

Red beats black (wins 21, draws 3, loses 12, winning factor 1.75)
Black beats green (wins 21, draws 3, loses 12, winning factor 1.75)
Green beats blue (wins 18, draws 6, loses 12, winning factor 1.5)
Blue beats red (wins 18, draws 6, loses 12, winning factor 1.5)


This means that with any choice of dice, the winning factor for you is at least 1.5. Consequently, they are the most interesting for us magicians. Spectator chooses first and you have in any case a very better die!
I have had these dice specially made by Steve Cormack. Anyone can order them here at https://trick-dice.com/product/michael-engel-dice/

Disclaimer: I am not profiting from the sale of these dice. I have found this particular group of numbers through trial and error. I assume I am not the first one to have found them, though you can’t get these dice anywhere else!