Numbers 19:2
זֹאת חֻקַּת הַתּוֹרָה אֲשֶׁר צִוָּה ה’ לֵאמֹר דַּבֵּר אֶל בְּנֵי יִשְׂרָאֵל וְיִקְחוּ אֵלֶיךָ פָרָה אֲדֻמָּה תְּמִימָה אֲשֶׁר אֵין בָּהּ מוּם אֲשֶׁר לֹא עָלָה עָלֶיהָ עֹל
This is the Torah’s statute that Hashem commanded, saying, “Speak to the children of Israel, that they should bring you a flawless red heifer that has no blemish and upon which there has never been a yoke.”
If the red heifer is flawless, don’t we know that it has no blemish? Rashi explains that “flawless” refers to the cow’s redness – even two black hairs would disqualify it. “Without blemish” refers to the usual defects that would disqualify a sanctified animal.