Based on parents, I would agree. Most of the time I would not be able to distinguish a Mottled Slate poult from a Slate poult from the poult color. Once in a while a TCM Slate will have a small spot of brown on it but not always. Not all TCM Slates are created equal since yours should be Bb1...
Did you show Porter the pics?
When a poult comes out an unexpected color, it is usually because one of the parents is carrying a hidden recessive gene or else the parents aren't what they are claimed to be. I have seen many turkey hatching eggs listed on eBay that the pictures of the parents...
According to the calculator, you have made a sex link hatch. The slate colored ones are supposed to be female Tri-Color Mottled Slates and the other color is supposed to be Barred Semi-Color Semi-Gray Dilute Lilac males.