Fruit Color in a Particular Plant Is Controlled by a Set

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 lower case letters do not produce any pigment at all.
-If a trihybrid plant (A/a;B/b;C/c) is testcrossed,what proportion of the offspring will have a fruit color phenotype that is different from both the trihybrid and the tester parents? (Assume no environmental effects.)

A) 1/8
B) 1/4
C) 3/8
D) 1/2
E) 3/4