First of all, do not let rude sales people put you off. Go right to the manager or say "I can see you're not interested in helping me. Please tell me who I should talk to about my project."
Having said that, I'm really not clear on what you're wanting to achieve. Are you sure you will be "pinning" your panels in the window frames? If so, how will you be using the tiebacks?
As far as color for the lining -- if the panels will be completely covering the windows and you want consistency from the street -- I guess go with the white, as the lining won't be seen from inside your home. If the panels will be pulled to the side with the tiebacks -- I don't think it matters whether it's white or off-white.
Why do you need the blackout lining? Especially with the tiebacks? At any rate, the blackout lining is all you need. It doesn't need to be sandwiched. I wouldn't use it in a kitchen, unless there is a real need to keep the room darkened. IMO, a good quality lining will protect your vintage fabric.
Please do a completed practice panel, including hanging and tieback, before using your special vintage fabric. It sounds like a special project -- you want it to come out just as you envision it. Good luck -- post pics.
Annie

Annie,
Thanks for your reply. I wasn't very clear in my description - the curtains won't actually have tiebacks at all; the panels will be inside mounted by using these little vintage flower pins to tack the upper two corners of each panel to the inside of the window frame. The flower pins are sort of like little decorative tacks, and were originally used to pin fabric tie-backs to the wall, but I'm using them in a totally different way. It's hard to explain w/o a photo, but because of the way my old house's double-hung bay windows are constructed, there is no other way I can see to do an inside mounted curtain, and I don't want to do an outside mount and cover the window trim. It's a vintage 50's kitchen, and the fabric is bright 50's floral, so it'll be almost like just tacking up a vintage tea towel (which is what I have in one window right now, so I can tell that it works and can see how it will look). I hope this description makes more sense. I don't really need to darken the room, but the lining will need to be opaque enough that you don't see the floral pattern from the street (some lining I saw was too sheer), and it needs to cut down on the sun enough that we can eat at the kitchen table w/o being blinded. :) Thanks for your reply; it sounds like I can just find a good-quality lining and go with that; no need for multiple fabrics. Thanks again; I'll definitely practice first and will post pics when I'm done.
Jenn

When you do decide wnat you want to use for lining shop around. I found Joanne's to be as much as $5 per yard more than other stores.

You want a good quality lining for your fabric, so don't skimp on the price or quality. I don't know about JoAnn's comparative prices, but I found their highest quality lining to be a good buy.

I made draperies for a 100-yr old house with beautiful wood trim. Since the windows were not too wide, I used a tension rod to inside-mount the draperies. I made them with a rod pocket and small header to nestle near the top, and I think they look great.

Maybe I wasn't clear - I found the EXACT same lining selling for $5 per yard less than Joanne's at another fabric store.

I would recomend tension rod too if it would fit. As for the lining, you could use interling also if the fabric is really bright and colorfull but I would'n worry about little color showing through the lining from outside, specialy at night.
Whatever you do, practice first and pin a lot.