ALLLL whites change with light, and a ceiling will almost always read cooler or deeper in tone. That is why a ceiling is usually painted a lighter color than walls. That said, every room WILL appear differently when painted the exact same white, or any other hue for that matter. All paints "change" with exposure to day light, ( at different times of day as well) and evening light, and can appear a different shade of that white or any other color on different walls within the SAME room. You will not focus on these subtle changes when the house is furnished.

All whites are not truly white. If you spread the BM fan deck of whites, you'll see that Moonlight is on a page in the section of the deck with yellow-based whites. How a color appears on a flat surface differs from how it appears on a celling, unless you get a ton of uplighting in the space. The color of your flooring can also affect how a color reads.

Is there a reason why you want all painted surfaces white? Unless this is an ultra-modern home, this choice can look sterile or as if chosen by a contractor rather than a designer.

If you're really unhappy, I'd recommend hiring a local color expert to come in for a quick consult. If a repaint of certain surfaces is recommended to achieve your goals, now's the time to do it.

Paints, even neutrals, have undertones. You should have a sticker on the paint cans, if you saved both of them, and see if they are the same, and if you don't understand them, take them to the store. If you are still concerned, call the store and see if someone can come out and look at the walls or see if they have suggestions..... most stores want you to be happy and will go the extra mile to trouble shoot.

Thank you for feedback. Let me ask this too... In living room and master bath I have European cabinets that I wanted lacquered or whatever process too achieve a very shiny look. They are also the same moonlight white- the painter told me if I lacquered them they would yellow over time so he chose to just paint them with a high gloss paint. These cabinets all read very yellow also... They were the last thing painted in house- same time as the walls. So should a high gloss paint read even more yellow?? My painter is going to come and look at paint with me, but I'm just trying to be prepared and do my research.
I had an interior designer help me with colors and I feel confident in his expertise with paint colors. And yes I am going for a modern look that is why so much white (there are a few rooms with bold accent colors tho). I just don't understand why no matter the time of day or location in the house, the walls are consistently yellow and the ceilings are consistently the color I wanted. It obviously is much more noticeable with more sunlight.

I have a feeling they used Advance, which is BM contractor's grade line, and it it has super dark base, to the point that it looks nothing like the colour on the colour deck.... keep us posted, very interested in your findings.

Advance is for cabinets and trim. Anyways light is bouncing differently off your ceiling and walls, plus it might be the same color but not formula, as other mentioned. The yellowing your painter was referring to, happens when you use a oil based poly. General Finishes high endurance poly does not change the color of your white.

I would sample & repaint the walls another white, if you don't like the current color.

This could be all about lighting and nothing about paint mixing. I have painted one room all the same color from the same can & it looked like completely different colors on different walls. For this reason I usually buy tester sizes first & paint an area as a test area on each wall if there is a specific undertone to the paint especially with beiges & whites. Some whites have a yellow, green or blue undertone, some beiges a pinkish or orangy or yellowish one. Whether the undertone will come out more is not something you can discern without doing that. Also the light changes throughout the day and in that respect you may only see the undertone at certain times of day. One thing I have found is that you can sometimes correct a color with an unwelcome undertone by mixing another color in. Again this is a task best tried first with tester sizes. To be successful you must add a tone in that balances out the tone you don't want to look more like what you'd hoped for. It's a very picky business. I once painted a room in a grey-green that in that light had a bit of a weird 'hospital green' undertone. I mixed a small amount of beige into the green and this remedied the problem. If you are good with colors you can usually figure out how to balance it. Good Luck!

Should the painter and/or paint company be responsible for the expense of repainting?

See you can see a little bit of difference in this pic. (Looks more obvious in person) The cabinets at the bottom are suppose to be lacquered- but they are high gloss. But look at difference between ceiling and wall- both flat paint and same texture.

BM has state of the art mixing system. The pigments going in are super precise, you can get the paint 2 years latter and it will be exactly the same. So I highly doubt it's their fault. And they would not be repainting it anyway, if the paint is off you (or painter/designer/contractor) supposed to notice it BEFORE it all goes on the wall and the store would fix it for you. Once it's on the walls it's between you and your painter. But do call the store and see what they can look up in their system. You need to figure out what happened. Do you still have all the cans on sight? If it's in fact paint from different lines, but you didn't specify the line, that can also be considered your fault. I do think there is a difference, but the way to check is to shine a very bright light into the corner where 2 paints meet and see if you can still see the difference. You have cathedral ceiling, so the difference in light hitting it should be less that if it was a 90 degree.

I agree but I noticed a real difference in color between BM ultra flat ceiling paint and Advance in semi-gloss in the same color AF-15, bought at the same time.

@Stephd, this is exactly my point. The base of all these paints are different (it's formulated different and not exactly pure white), but the AF-15 (or whatever number) pigment is exactly the same. They don't have a way to adjust for a different base. So you end up with different colours. This is only noticeable in whites, but it's a real difference not just light and angles and such... If your base is yellow and you add magenta you end up with orange, if your base is cyan and you add exact same magenta you end up with purple blue (it's obviously a very exaggerated example, but just to illustrate my point). So you can come back in 2 years and get the same Advance and will match your Advance you got now, but the 2 paints you got now don't match. This can create really tricky situations obviously.

Again, no one can control the way the light hits the paint regardless of how precisely the paint is mixed. Some very astute professionals realize this and some do not. The types of paint mentioned here may very well reflect differently in a store or even just looking at a small sample it's hard to tell really. You can mess around with lighting but natural light is pretty hard to control without blotting it out. I would suggest you talk to the painter/store about it and if it really does bother you and takes away from the look see if you can figure out how to correct it. After all it is only paint - but yes it does cost more money. If you are willing to repaint you can use testers to try this but I think you should be careful just paint a test color on small discreet area or even a piece of poster board from the dollar store placed in the area you want to repaint. You need to look at it at different times of day to make sure you just lose the yellow but don't lose the undertone you actually wanted. I would suggest getting some other similar but much less yellow paint samples then make a tester of one you like after looking at it in that area you want to repaint. You may be able to save money & just mix it half & half or some ratio with the new test paint & the old paint to correct the color to what you want. A trick is to take some Chinet paper plates and paint the sample mixes on them then hold them up to compare which mix ratio works best - half & half or 2 parts to one part etc. Use cheap dollar store measuring spoons to measure - like 2 tablespoons this white & one tablespoon that white. Make sure you write the paint names and ratio used in the mix on each paper plate you test it on. When you get the right ratio do a sample on the actual wall or ceiling or paint a poster board to hold up in that area to see how it looks. If you don't want to repaint you can mess with lighting as I say, it may help.