Great reference site, but in this case, I believe the nudibranch photographed is actually mislabeled as the Tricolor. From what I can see it's actually either
Chromodoris elisabethina or
Chromodoris annae.
Either way, these guys would be incredibly difficult to feed, as
C. elisabethina feeds on specific sponges, and
C. annae feeds on specific sponges and ascidians (tunicates).
http://www.seaslugforum.net/showall/chroelis"C. elisabethina is one of a group of black-lined species which feed on both orange-red sponges of the genus
Negombata and blackish or brownish species of the family Thorectidae. I can't be sure if the animal in the upper photo has been eating the orange-red sponge, because there are other sponges present in your photo as well, but I can definitely agree the animal in the other photo has been feeding on the pale brownish sponge which I am pretty sure is a species of thorectid. It is certainly suggestive that the nudibranch with the pale watery orange colour in the mantle is eating a sponge without any red-orange colouration. We don't have enough photos of this animal on their food to see if there is any correlation between animals with bright orange colouration and orange-red sponges but it would be worth looking out for."
http://www.seaslugforum.net/find/chroannaThis one has links at the bottom with discussions of various foods it eats, but it's not all in one nice paragraph like I quoted above.
