What Am I Riddles

Question: What can be white and yellow at the same time?

Question: If you aim to give us a shot, we'll riddle you.

What are we?

Question: I cannot be seen, cannot be felt,
Cannot be heard, cannot be smelt.
I lie behind stars and under hills,
And empty holes I fill.
I come first and follow after,
End life, kill laughter.

What am I?

Question: Skinny I am fast,
fat I am slow,
but I'll still delight you from your eyes to your nose.

What am I?

Question: What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?