The Prophet (peace and blessings be upon him) said:
"The blood of a whitish (sheep) is purer in the sight of Allah than the blood of two black (sheep)."
Hadith Referenceصحیح الجامع الصغیر / حرف الدال / 3392
Hadith Gradingالألبانی:حسن
Hadith Takhrij[طب] عن كثيرة بنت سفيان. الصحيحة ١٨٦١.