Help for the needy... please?

Am trying to make a wildcard IF formula to work. The sample below doesn't
work because IF formula can only match by one word and not a word within a
few. I'm looking for a formula to detect the keyword "yellow" in each row in
column B and add in 15 working days for delivery date. Here's the table I'm
working on:

A B C
4/10/06 yellow shirt =IF(B2="yellow*",WORKDAY(A2,15,0)-1,"")
4/10/06 red hat
4/11/06 yellow pants
4/10/06 yellow belt
4/12/06 blue tie

Thank you in advance for any kind souls out there who can help...:)
--
Goh Han