How to make our Black pigs skin darker

I have two hogs.. Both Hamp Cross. One is a tad darker than the other but they are very very pale... I have recently let them out to sun in the late afternoon for a hour or two, but i do not see much of a difference.. Any ideas? Has anyone use the Quik Black shampoo? Does it work on pigs?

When you turn them out in the afternoon spray mineral oil on them. That will help just take some time to get them to darken back up.