Not to be argumentative, but Maltese did come in other colors at one time. Whether any of those genes have survived in the bloodline to this day, I don't know. It is possible though, and a black Maltese would be rare.
"From 1902 to 1913 The Kennel Club offered classes for Maltese dogs, other than white. The first entry made under this classification was made in 1908 and the last was made in 1913. The colored Maltese differed from the white variety. The English standard for the Maltese called for the white variety not to exceed 12 pounds. The colored variety could not exceed 8 1/2 pounds. All colors were admissible into the colored classes. The white variety were required to be pure white. Besides the size difference, there were other variations between the two varieties. The colored coats were coarser textured than the white coats. The head of the colored Maltese tended to be shorter muzzled and broader skulled than those of the white Maltese."
From this link...
The Maltese Breed History