Unless There is something I'm not aware of, I never heard of night and day Nasturtium. I have never seen 2 colors of nasturtium on the same plant, Some blossims may fade in the sun or some may darken as they get older but they are just slight variations of the same color

ya, there is one called night and day, here is a link.

http://www.territorialseed.com/product/725/133

i am assuming that it will produce two different colors on the same plant, because they always advertise it like that. after all, if there are two plants, why would they put two different kinds of seeds in one package? that doesn't make sense, they can just sell those two different color nasturtiums in two packages.

Look at your own blurb--It says they are covered with a flush of flowers of EITHER color. That means 1 plant one color or one plant the other. There are 2 varieties in your package of seeds. Both will not grow on 1 plant.

They do probably sell each one separately as well as the blend. This is just a blend that one seed company put together and you must admit they are very pretty together. It is not unusual--seed companies often do that.

Night and Day is a blend, as oilpainter said. I saw packets of them in a local store yesterday.
The reason companies offer a blend is because some customers prefer that. It is often cheaper to buy one mixed packet than two or more packets of separate colors. With a premixed blend, you know the plants will bloom at the same time and look good together. There's another nasturtium mix I've seen called "Caribbean Cocktail" that has at least three colors together, and "Alaska" is usually offered as a mix of colors.
The downside of buying a blend is that you sometimes need to plant the entire packet to get all of the colors in the mix. If you only plant a few they may be all one color.

I have a nasturtium in flower now with two seperate colours of flower on the same plant(YELLOW AND ORANGE)
- it also has variagated leaves.This is a 'sport', I am sure.