1998 HK151 has the lowest, and thus bluest measured B-V color index of any TNO. On May 24, 2000, 1998 HK151 set a TNO record low B-V of 0.51. Reddening of the spectrum is caused by cosmic irradiaton by ultraviolet radiation and charged particles. Becoming bluer in the spectrum is caused by impact collisions exposing the interior of an object.
Based on an absolute magnitude (H) of 7.62, 1998 HK151 is estimated to be between 85 – 190 km in diameter.