(a) Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saw two yellow garments on Abdullah bin Ja'far (may Allah be pleased with him) while he was in ihram, and said: What are these garments? Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said: I do not think that anyone is going to teach us the Sunnah. So Sayyiduna Umar (may Allah be pleased with him) fell silent.
(b) It is narrated from Nafi' that the wives of Sayyiduna Ibn Umar (may Allah be pleased with him) used to wear safflower-dyed (yellow) garments while they were in the state of ihram.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9115