It varies from breeder to breeder and the confidence in the show prospects of each kitten may vary. As kittens some things can be identified, but others develop over time. Read the standard in the association in which you plan to show and compare this to the kitten.
Nothing can beat attending shows and seeing successful show kittens and cats.
Although there are exceptions, male bicolors seem to do best. Talk to those who have successfully shown close relatives of these kittens to see what you should look for in these kittens. Keep in mind that show means show prospect, since much goes into show success and promising kittens can develop into disappointing show adults. It varies from breeder to breeder and the confidence in the show prospects of each kitten may vary. As kittens some things can be identified, but others develop over time.