Ask any designer, white isn't just white.
There are so many variations on any neutral, but white and black are the most infamous for confusion and "color clashing." Just search "white" through Pantone's color finder and you'll see what I mean. You come up with a whole array of colors that all contain "white."
You might have noticed that when ordering or searching for wedding stationery, you are given a few options for white: ecru, ivory, soft white, white or bright white. These pretty much exist on a scale of having a warm undertone to no undertone at all. But, with all the options, how do you decide which will fit your wedding?
Which one is the right one for you?
We tend to think of off-whites or ecru colors as warmer and even more traditional. But, that isn't necessarily true. If you are using ivory, off white in your design details, go with ivory or ecru. Even bright pops of color can look beautiful printed on ecru papers. But, some light or light-bright colors like yellows, light pinks or light oranges might not print with high enough contrast to look good on ecru. That is why test printing is so important.
Brighter whites, on the other hand, have a reputation as more contemporary. But, bright white wedding papers can be just as formal and traditional as ecru ones. Bright or lighter whites allow for higher contrast and more versatility. But, if you are having more off-white or ivory details, things might look a little off. Going with a regular, classic or even soft white will avoid this to an extent. Those more neutral whites are so much more versatile.
You should ultimately make the decision based on the other colors and textures you will be including in your wedding papers and details. If you have very bright colors or are looking for a high contrast look, go with bright white. If you are using a lot of warmer whites or ivory details, ecru might be the right choice.
Keep It Consistent or Consistently Inconsistent
I actually love the look of mixed whites. Some white, some ecru in the invitations and details. But, this idea it has to be executed correctly and universally throughout the event. Mixed whites can add seemingly effortless elegance. But, it is easy to go wrong if you don't mix it up enough (or, if you mix it up too much).
If you want to select one white, try to to keep it consistent by selecting a paper stock and keeping it the same throughout the event. Your printer can help with that. Otherwise, the clash of the whites will be a subtle, but pervasive eyesore in throughout you event and your wedding photos.