一も二も無く[ichimonimonaku] unhesitatingly
一言二言[hitokotofutakoto] a word or two
一石二鳥[issekinichou] killing two birds with one stone
一二に及ばず[ichininioyobazu] right away
一姫二太郎[ichihimenitarou] It's good to have a girl first and then a boy

うり二つ[urifutatsu] as alike as two melons (two peas in a pod)
黄道十二宮[koudoujuunikyuu] twelve signs of the zodiac
二度[futatabi] again
最小二乗法[saishounijouhou] least-squares method
三十二分音符[sanjuunibuonpu] 32nd note

茜色[akaneiro] madder red
暗褐色[ankasshoku] dark brown
暗色[anshoku] dark colour
暗赤色[ansekishoku] dark red
異色[ishoku] singular (esp. artist, artwork)

からすの濡れ羽色[karasunonurebairo] glossy black (hair)
烏羽色[karasubairo] glossy black
炎色[enshoku] flame (color, colour)
鉛色[namariiro] lead colour
鴬色[uguisuiro] greenish brown