Fruit color in a particular plant is controlled by a set of three QTLs (quantitative trait loci, or polygenes) that work in an equal and additive manner. Each QTL has two alleles (i.e., A and a); each allele represented by a capital letter produces one dose of yellow pigment, while alleles represented with lowercase letters do not produce any pigment at all. Assuming no effects by the environment, how many different shades of yellow fruit color are there?