I have a good question..... I bred my bay mare to my cremello stud. Now...by most all standards genetically she would only throw buckskins with him. Well...last year she threw a gorgeous Palomino. This year.....the foal was silver (His g-grandfather is WGC Silver Design). When he started shedding off his foal coat he turned buckskin....now...he is shedding off to his winter coat and has turned an almost chocolate color with fine flea-bit silver. I am clueless! Here is a pic of him.
My horse color genetics are a bit rusty, so please, bear with me.
The Palomino is easily explained. A Cremello is a red horse with two cream dilution genes. Red is recessive to black, and though bay is a black-based color, you only need one black gene to produce it, so the mare is carrying a red gene that she clearly passed to that foal. Red from the dam, red from the sire (as that's the only thing he has to give) plus one cream gene from the sire and there you go, palomino.
If I were to try to name your current colt's color, I'd call him a smoky black, or maybe a smoky silver black(?). Your mare is a bay, which is a black horse with an agouti gene. Agouti is dominant, but the mare could be carrying a self gene as well. Since agouti really only affects the black pigment in the coat, you can't tell by looking if the cremello has agouti. What I see is black from the dam (and red from the sire, of course, though you can't see it), possibly self from both parents, and cream from the sire. On the other hand, he might be a very sooty buckskin - not all buckskins are golden.
Just to point out that the color calculator is not very accurate because there is no way for it to know the exact genetic make up of your horses. So it is a guess at best.
Just want to second Bunnylady's post. This colt could be smokey black or very dark buckskin. Once he gets is proper coat in you should know for sure.