Compare Ranges/Return Specific Value for Matching Cells

I'm stumped on this two-part issue and sure would appreciate any help.

First, I have a range of cells (a1 through a5) which each contain an individual number.

a1=196 and b1 presently blank
a2=4 and b2 presently blank
a3=67 and b3 presently blank
a4=669 and b4 presently blank
a5=345 and b5 presently blank

I want to compare it with a second range (a16 through a20) and see if any of the cells have the same number.

a16=7 and b16=red
a17=222 and b17=blue
a18=669 and b18=yellow
a19=67 and b19=white
a20=781 and b20=red

Secondly, if any numbers between the two ranges match (i.e. A3 and A19 are both "67"), I want to copy the B column value for the number in the second range into the B column value for the matching number in the first range. Here's what the end result would look like:

a1=196 and b1 stays blank
a2=4 and b2 stays blank
a3=67 and b3 becomes "white"
(because white is the B column value
of the matching number in the second range)
a4=669 and b4 becomes "yellow"
a5=345 and b5 stays blank

Any ideas on how to accomplish this? Thanks so much!