Usually with punnet squares, a letter will represent the gene at a specific loci. A capital letter represents the dominant gene, and the lower case letter represents the recessive gene. For albino, AA would be a normal, Aa would be a het, and aa would be an albino. Some people will use other symbols to signify which gene is dominant over the others, like on the Sutherlands site where a+a+ is normal, and aa is albino.

-Evan