Having just done this last month...
Leave the baby's SS# field blank, they know you won't have it yet.
For height, put the baby's length at the most recent Health Visitor clinic or Doctor's appointment.
For hair color: he must have some tiny bit! Look close and use your best guess, or, if you really, really feel like there's not enough to work with, leave it blank. At the consulate, they'll ask you again, and you can discuss with them. I put light brown, though it's anybody's guess whether it will darken up in future.
I put this in another thread, but I'll add it here.
1. Make sure you find the line for US citizens. It's much shorter, so much so there may be nobody in it, so you won't notice it. The long line you will notice is for everyone else. Ask the nice security guard if you don't see the sign for the citizens line.
2. Expect US airport type security. Everything you are carrying goes through the xray, and you go through a metal detector. You don't have to take your shoes off, but I was asked to put a few drops of the liquid in the baby's bottle on my finger and taste it. (OTOH, they didn't find all 3 bottles that were in the diaper bag!)
3. There are TWO flights of stairs to reach the room you need to go to. And from there, 2 flights down to the restroom/baby change area. There were no elevators or escalators, although there were employees on the steps outside. Not inside though. This may change due to the new security huts that were under construction, which looked nearly finished.
4. your appointment time is not a firm appointment for just you. It's a cattle call, with lots of people arriving at that time. Arrive a bit early, so that you can get into the line at window 1 ahead of as many people as possible that have the same 'appointment' time.
Don't know where you are coming from/to, but for us, we timed it to arrive in London in time to make our way to Chinatown for lunch, then a stroll from Leicester Sq area to the consulate was long enough that our little guy napped. Our 'appointment' was at 2:15 and we left the consulate about 4 pm, which is just as the evening rush hour on the underground begins to build. We went to Oxford St, and had dinner at one of the department stores (because I've noticed they always cater to families: high chairs, changing stations) and then window shopped until we felt the underground would be less crowded closer to 7.
