Artisans in the fifteenth century discovered that they could make different colored glass if they used certain natural elements. They would test different types of metals to add to the silicate while it was hot to see what color combinations they could come up with. Glass was a good medium since it is relatively stable and holds the color once it is established. Look at some of the plate glass windows created hundreds of years ago and it is evident the masters knew how to form a multitude of colored shards into something beautiful that would last.
The advent of neon gas in closed glass cylinders had a similar effect. People saw the pretty red color and the stability of the design and wanted to see what they could create.
Neon signs don’t just come in all the colors of the rainbow (there are only seven after all), but as many as imagination will allow. But not all ‘neon’ signs are filled with neon gas either. A designer determines the effect he or she wants, and they use a 'recipe' of selected gases, glass and coatings painted or baked onto the interior of the glass tubes (much like pane glass designers used) to create rich colors.
You may ask, Not neon? What!? False advertising.
Okay, so you didn't think that. Most people know that gas blends are used to create the different colors shown in a given neon sign. Most commonly used is neon and argon gas. Neon gives an orange-red color. Xenon produces a purple color. Helium yields a pale pink flesh color. Krypton gives a platinum color. Filling a clear glass tube with argon gas produces a faint purple color, but add a touch of mercury and you get a deep blue. Sometimes an opaque instead of a clear tube is used and sometimes the tube itself is colored to add depth to the colors.
Neon is in the name because it was used by a good promoter (Georges Claude) to sell his neon lamps (although those lamps probably did contain pure neon). But who was going to be content with just reds and oranges? Claude and more recent manufacturers had to determine ways to provide more color. So, they did and now we have a richly colored neon sign history.