What color will these Guineas be when they grow up?

Here's what I see.

I agree with Ash's ID on colors... and I think I can see some Pied Pearl Greys in the far back corner, can't see their head stripes tho. They could be more Teddy Bears. All of my keets with Teddy Bear markings (solid colored down) grown a few white flight feathers and a splash of white feathers on their chest when mature (which is what I refer to as lightly or slightly Pied).

Be careful about raising young keets on shavings, they can eat them and die from getting impacted. Straw, well textured paper towels or rubberized shelf liner all work great for me for young keets.

Teddy Bear keet, not Guinea. "Teddy Bear" is just a term some breeders have coined for the pattern of the keets' down, which is usually a wider middle head stripe with just one thin tan stripe at the outer edge (if visible), and more of a blended/mottled body color all over (except the belly) rather than the normal 2 tone striped pattern for fully pearled keets. They will feather out as normal looking slightly Pied Pearl Greys (like I said, usually with white flight feathers and a splash on the chest).

The width of the head stripe can vary, depending how Pied the keet is. Sometimes there won't be a thin stripe at all on the sides of the head. The slightly Pied keets that are mostly brown with just a little white on the sides of the face and wingtips are the keets that were first called Teddy Bear keets, but the term refers to all keets hatched with solid (blended/mottled) down pattern, regardless of color (not to be confused with the non-pearled varieties like violet, copper, slate, pewter etc that are complete void of all stripes as keets). Once the TB keets lose their head fuzz you can't tell they ever hatched any different looking than a Pied Pearl Grey keet that hatched with normal markings (same with the other fully pearled colors that hatch with TB patterned down like Lavender, Cinnamon, Buff Dundotte etc).

I have yet to come across a clear explanation of why it happens, but IMO the Pied gene plays a part in it, because that pattern only shows up in my flocks that contain Pied breeding stock.