Great question - these genetic traits are definitely fun to study!  I think you are likely seeing the results of the silver/gold gene.  The Silver allele (S) is dominant to the gold (s) allele.  Because of other genes, you can see this white ("silver") color in the penciling of the Brahma.  The Rhode Island Red is s/s (gold or red).

This is a bit of a special trait, because the gene is on the sex chromosome.  This is similar to X-linked traits in humans, except it is reversed in birds.  This gene cross is used with a lot of the commercial brown-egg laying chickens.  In the case of this chick, I am fairly confident it is a male.  If you had hatched more chicks from this cross, the females should be red.

Some of the other traits (like penciling) may show up later, but may not be fully expressed.  In many of these crosses, the mature male is mostly white, with some patches of red coloration, often on the wings.

It will be interesting to see how it develops with age!