May even have been cremello.

On some pedigree sites she is shown being sired by Harviestoun Pippin and out of Wells Stella. That information is most likely incorrect or at least her dam, Wells Stella is wrong.

Why? Wells Stella was homozygote on the extension gene (E/E) meaning that it was impossible for her to throw a red based foal (palomino, or cremello for that part, is the cream gene acting upon a red base), regardless of sire. Neither did she seem to carry the cream gene otherwise she would have foaled more cream or at least the gene would have been found in later generations (if some of the foal would have been smoky black).
And, on top of all that, Deldon Crystal was an Inspected Stock meaning she had no known pedigree but was of shetland type.