White… that color bereft of colors or the color that is a combination of all of the colors depending upon what kind of colorspace you are talking about. One of my most favorite demonstrations in college physics was the additive color mixing example where they have red, green and blue as separate color discs, then they bring them together and in the middle you have white.
That said, in nature, one rarely sees truly white images. One of the things I’ve been doing lately is making images representing colors (Yellow and Blue), (Green) and then mapping out the representative colors in 8-bit colorspace as seen below. The shocking thing is how many other colors appear in images that are consciously at least, dominated by one color. In the case of the Yellow and Blue post, all of the browns and rich hues of blue and in the Green post, the browns, violets and whites. In this image, when made at 35,000 feet I saw mostly white. Looking at the image now and reducing it to 8-bits shows just how blue the scene was. Kinda a fun exercise.