You're describing the colour I wanted for my bedroom. A bit difficult to get a warm white with cool undertones though. I settled on BM Whitewater Bay OC-70 but it veers more peachy-pink than lilac pink, I think. Have you looked at BM Oyster 2115-70 and BM Vintage Taupe 2110-70? Good luck with your search. Totally relate to "I will know it when I find it." :)

Thank you for your quick response! Yes, I know it is a contradiction to want a warm white with a cool pastel undertone; but it has to be out there somewhere! This is for my master also. I actually mixed two colors in an upstairs bedroom that we made into our 2nd floor den when my daughter left for college to get a smoky white-gray with purple undertones and I love this color, and thought of trying to re-mix colors to try and get it again, but it faces totally opposite of the master that I want this mythical elusive color in, and gets different light, plus I don't even remember what I mixed to get this. Thanks so much for the suggestions and I am going to the BM website to check both! Did those come close to what you were envisioning for your room?

I am not sure if it has any pink undertone, but BM’s Ballet White is nice.

Don't trust your monitor to show you the accurate BM colour. I'm on a Mac which supposedly renders true colours and every time I've gone to the BM store to check out something I liked on screen, I was flabbergasted at the different colour I found in store. If you shop around looking at colours on screen, you'll be wasting a lot of time. It's one thing to read colour descriptions online but another to look at colours online searching for "the one". The first can be helpful in figuring out a colour family or direction but the second is an exercise in futility. Unfortunately, I haven't painted my room yet so can't say for sure I found "the one".

Another tip: check out Samplize for colour testing. A lot of Pros here recommend it as it simplifies the colour testing process.

Good luck! Hope you keep us posted. :)

ETA: My worry about a warm white with cool undertones is that it will look dirty or muddy. Other BM colours you might want to check out: White Blush-904 (possibly too yellow), Pensocola Pink - 1184 (too pink) and Venitian Marble-12114-70 (might not read white at all). If you go to a BM paint store with helpful staff, you might be able to get them to test mix a couple of colours. One local BM store had offered me this. Have you looked at other paint companies? I'm wondering if Farrow & Ball would offer you something you'd like. I remember getting their paint samples years ago and being confounded at their "muddiness". Very "dusky" colours that seemed to go both warm or cool. On my screen, their Great White might be what you're describing. Who knows what it actually looks like irl. :)

Why not Dreamy Cloud BM stop trying to get a warm white with purple undertones just look for anyw white with that ubdertone.

Thank you all for the great ideas and suggestions! I am going to check out all of the color choices that you have given me. I will keep you all posted on the outcome!

I have a couple more to suggest. There was one colour I was very tempted by but it seems I didn't keep the paint strip. I'd knew I'd recognize the name so I browsed the BM site.

Pink Essence - 881. Might not be warm enough for you though. It reads white with a hint of cool pink, if memory serves. It was pink without being pink, you know? Perfect for when you're sharing a bedroom with someone who doesn't want pink. ;-)

Hampshire Rocks - 1450 - might read too grey?

Calm OC-22 - slight hint of purple - it reads beige on the OC strip but I see some purple in it.

I have the strip with Dreamy Cloud 2117-70 that Patricia suggested. Looks quite nice but don't know if you'd find it warm enough. It looks pastel-ly next to Hampshire Rocks.

That's another thing with this little paint squares on a strip. We can look at them next to each other to compare but you have to consider each one individually in the room, in all types of lighting. Quite a hoot finding a colour. :P

Again, good luck, and I look forward to hearing your choice.

I see this is an old post but try BM OC-71 Sanddollar

I also suggest SW Eider White. I used it in multiple bedrooms in a former home and it is a color that changes with the light. It would show lavender or pink undertones depending on how the light hit it. It tends gray but is not really a gray either. It has warmth to it.