I mention only egg and flour below. Colours and flavours may be added, but these are a distraction and to my mind, normally to be avoided. Your eggs and flour, therefore, are of the utmost importance. It may seem silly to state, but try to make sure the yolks are as dark a yellow as possible. Pale pasta looks, and somehow even tastes, insipid. I use Italian eggs whose hens were fed on God-knows-what (I believe a mixture of purest corn and carotene), but they make my pasta a glorious buttercup yellow.