I think all the colors exist between white and black. The lighter and brighter color shows higher vibrational frequency; whereas, heavier and darker color shows lower vibrational frequency. In another term, thing that vibrates with higher rates is in color of lighter and brighter because of increased frequency. And, that vibrates with lower rates is in color of heavier and darker because of decreased frequency.

With the same understanding, for the highest healing energy, the color should be lighter and brighter due to its higher frequency.