The de Grey-Haugstrup graphs are two 6-chromatic graphs on 47 and 48 vertices that are unit-distance in 3 dimensions (de Grey and Haugstrup 2020).
The 47-de Grey-Haugstrup graph was also used by Haugstrup (2026) in the construction of a the 21217-vertex Haugstrup graph.
The 48-vertex 6-chromatic graph with graph dimension 3 is a faithful graph (i.e., all vertices separated by a unit distance are joined by an edge) with 152 edges. As it turns out, 3 of these edges may be removed while still preserving chromatic number 6. Exact coordinates were found for the vertices by E. Weisstein (Jan. 6, 2026).
The de Grey-Haugstrup graph on 47 vertices is implemented in the Wolfram Language as GraphData["DeGreyHaugstrupGraph47"] and GraphData["DeGreyHaugstrupGraph47"].
." Geombinatorics 33, 110-115, 2022.Haugstrup,
A. "A Tetrahedron-Free 6-Chromatic Unit-Distance Graph in Three-Dimensional
Space." Geombinatorics 35, 2026.