She's the dam of a palomino, if I got it correct?
If so, she only has one copy of grey, so a 50% chance her foals will get the grey gene from her.
Grey is not a color, in a sense, because ANY color horse can be grey. Grey is a modifier that causes horses to loose their color as they age. So the mare is a color under that grey, but what it is, can't say without seeing pics from when she was young or color testing her. But I can say she has at least one chestnut gene since she had a palomino (which is chestnut with cream). The cream gene probably came from the palomino's sire, although it is possible that the mare is also cream (buckskin, palomino, ect).
The buckskin stallion also must have a chestnut gene. It takes two chestnut genes to be chestnut, so the palomino had to get one from each parent. If a horse only has one chestnut gene, the horse will be black based.
Mare is ?e (E= black, e= chestnut) Gg (one copy grey) and both agouti (turns black to bay) and are cream unknown.
Stallion is Ee (black horse) A? (at least one agouti, turned his black to bay), Crcr (one cream, turned his bay to buckskin) and no grey.
The foal she's carrying has a 50% chance of going grey.
Without knowing the exact genetics of the sire and dam, possibilities are: black, bay, chestnut, smokey black, buckskin, palomino, and since it's possible she COULD have cream, any of the double dilutes.