M.B.
L.,
Maybe have a game of pin the tail - updated! Your guests can hold a toy with a blindfold and see if they can get it together. Maybe use toys that your son is unable to use for just this purpose - that would be enlightening for your son's guests.
Your son CAN see colors - just not definitive shapes, correct? Maybe have poster board in bright colors (well, I wouldn't go neon, but maybe he might respond to that too?) Decorate for HIM!
We held off on all sugar, so we didn't have cake for my son. A cake sounds really over the top for your son - but your guests will enjoy it.
Sounds? Lullabies are good - they're not just for naptime! Also WeeSing - a lot of songs that your baby will be able to relate with given enough repetition, as well as your GUESTS (memory is a fun thing).
Touch - hard to say there, he's getting into the clingy stage if he's like a lot of other kids. He may not want to leave you. Getting him acclimated to other voices would be a good idea.
Good luck! I'm sure you'll get a lot more ideas!
M.