When you're working on your map design, it's important to be aware of the different colour models, how we can define colors or described them, and when it might be useful to choose one over another. If you're choosing a colour in the software, so in ArcGIS for example, there's different colour models that can be used to specify the same colour. So for example, we can use the RGB colour model and I'll explain each of these more in a minute, but that's the red, green, blue, and so we can choose a blue colour using an RGB colour model. We can also use an HSV colour model, and we can use a CMYK colour model. So those are the three color models that are available inside our GIS. So what I want you to notice here is that they're all describing exactly the same colour of blue. So the colours are the same in terms of how they're going to look on the map, but it's just a different way of describing that color or defining it based on which color model you want to use. The RGB colour model is based on red, green, and blue, hence RGB. You're probably familiar with this. It's a very common one. It was designed originally to be used for things like television screens, and computer monitors, and now on phones, that basically you have these pixels that are able to show combinations of red, green, and blue in varying levels of intensity, and if you mix those red, green, and blue colours to create other colours. So, here we have the main colours the red, the green, and the blue. If you completely mix red and blue, you get magenta. If you mix blue and green, you get cyan. If you mix red and green, you get yellow, and if you mix red green and blue completely together, you get white. So you can think of these as additive colors, like you're combining different amounts of light of these different colors. So, if you had a complete absence of all three of them, you would have black, if you've completely added all three of them together at the maximum amount of intensity you get white, and then you can vary the amounts of those in-between to mix to get other colours that you can define. So, I don't mean for this to show that these are the only colors that are available. Essentially, anytime you look at any kind of a screen now, all of those colours that you're seeing are based on mixtures of only red, green, and blue, just based on different amounts of intensity of them. One way of thinking of this that I like that I just got from Wikipedia actually is this idea of thinking of them as dimmer switches, so if you had, you're able to slide a dimmer up and down to vary the intensity of each of the red light, the green light, and the blue light that you can do that or the monitors doing that or the screen whatever in order to be able to mix those colors together. So why this relates to map design in particular is that if the final output of your map is going to be on a screen, then it probably makes sense to think about your colors from the point of view of red, green, and blue because that's the color model that was designed to define colours for screens, and if the final output of your map is going to be on the screen, then why not use the same color model that matches that. The traditional way of defining red, green, and blue is with a range of 256 different values, that's based on an eight bits numbering system or range of values. So if you have 256 values that start at 0, then you have a range of 0-255. So if you have red, green, and blue that are all defined as 0, 0, 0 then you will have black. If you have 0, 0, 255 in other words red is 0, green is 0, blue is 255, which is the maximum, then you will have the sort of strongest blue that you can have. Then we can do the same thing with green. So we have all green and nothing for the red and the blue there, we can do the same thing with red. So I'm just trying to show you that you are able to get these sort of maximum values based on that, but we can also construct what would be called a colour cube based on RGB. I think this is a nice way of being able to show that you actually do get this gradation of colour values based on just mixing these three different numbers for red, green, and blue. So I hope you're able to see that as, yes, we have a pure yellow here, and up here kind of cyan here, but there's this gradation of colours from one to the other. Of course, this goes in all directions. So you're able to get sort of purples, and blues and browns, and reds just by mixing these three colors together. This is just one way of defining colour based on this idea of red, green, and blue. So this is the colour cube just without the transparency. You can see that these are the color selector values if you were doing this in ArcMap. So you are just getting red, green, and blue, and we have values from 0-255 to define those. So that's the yellow there, a red there, and so on. So, just a way of being able to show that or to visualize to think about it when you see that little dialog box and you're looking at those values and you're wondering maybe why they don't go from 0-100 or something like that, that's why as it's based on its eight bit color scheme. It's kind of a really ancient now way of numbering things, but it's just being carried over from year to year and so it's still there.
