Reference for Pesachim 148:5
והא רבא איקלע לבי ריש גלותא וטפלו ליה בר אווזא אמר אי לא דחזיתיה דזיג כזוזא חיורא לא אכלי מיניה ואי סלקא דעתך כבולעו כך פולטו מאי איריא כי זיג אפילו כי לא זיג נמי התם בחיורתא דשריר
Now should you think, as it absorbs, so it exudes, why particularly when it is clear; [it is permitted] even if not clear? - There it was [prepared] with white flour, so that it [the paste] is compact.<span class="x" onmousemove="('comment',' Which prevents the blood from oozing.');"><sup>10</sup></span> Now the law is: [a paste] of finest flour, whether it looks red or does not look red, is permitted;<span class="x" onmousemove="('comment',' Even in the former case we assume that the blood which the paste absorbed certainly oozed out, the redness being a mere hue which it leaves.');"><sup>11</sup></span> [a paste] of white flour: if it is as clear as whit glass, it is permitted, if not, it is forbidden; [a paste] of other flours: if it looks red, it is forbidden; if not look red, it is permitted.