Please note being colorblind doesn’t mean everything is in gray, that’s only in very rare cases and isn’t the case for dogs.
Most eyes see color by having cells that are sensitive only to certain wavelengths of light. This is normally a bell curve, which means a those cells are sensitive to a larger part of the spectrum. There can also be overlap in the spectrum different cells are sensitive to.
The concept of color isn’t a physical thing, the cells just respond to parts of the spectrum. The brain however interprets those signals and assigns concepts to those signals. This is what we call color. At a young age we teach our children if you see this signal we call this red, this signal we call blue etc. Because this only happens in the brain this is somewhat subjective and we can have colors that aren’t directly related to a wavelength of color (like magenta, but also stuff like white, black and metallic colors for example). This is also why we can trick our brains to see a color, just by mixing around some signals. This is how stuff like monitors, TVs and colored led lights work, they just emit enough energy in the right parts to trick our brains into thinking it’s a certain color. Back in the day we didn’t do this very well, which lead to “harsh” light, which looked right on a glance but caused headaches and fatigue or even pain when looking at it for a long time.
There are different kinds of color blindness and to different degrees. Online are simulators where you can see how people (or dogs in this case) view the world. There are also animals that are sensitive to a greater range of the spectrum, in their eyes they would think we were the colorblind ones. So colorblind doesn’t usually mean literally can’t see any colors. In reality a lot of people are slightly colorblind and would never notice it. It’s like the stereotypical discussion of the wife wanting to paint the wall eggshell instead of off-white and the man not being able to see a difference between those two.
More reading: https://en.wikipedia.org/wiki/Color_blindness
Round connectors were absolutely used to transfer data, for example audio and video in the form of RCA plugs and many other examples back in the day. Another example is coax cable for TV signals (both analog and digital) and also LAN.
However the lack of distinct interface channels leads to a bottleneck in bandwidth. So as the need for bandwidth increased many of those were replaced with multi pin versions. This is much harder to do with round connectors and there isn’t that much benefit, so they mostly got ditched.
However round connectors still have their place, for example tiny little coax connectors found in many devices to carry signals. Wifi antennas and such are connected this way.