There are 12 tones in our Western musical system. There could be more, there could be less, but in Western music, the use of 12 tones is the given. We are given 12 tones to create music with. A tone can also be called a pitch. Pitch is the relative highness or lowness of a tone.
This 12 tone system is called Equal Temperament (equally spaced half steps). Just Intonation is another system of tuning based on the pure vibrations of nature (where the harmonics of a given tone are the basis of the tuning - only that key is in 'perfect' tune).
The 12 tones lie one-half step to the next or previous. On the guitar, one half-step is one fret. Every next tone (fret) is one half-step away. Half-steps can also be called semitones (where a tone is a whole step, which equals 2 semitones). We will be using the term half-step in every instance.
For whatever tone we put at one, we cycle through the 12, then back to the original (whatever we put at one). Any of the 12 tones can be placed at 1. After 12, we go back to 1.
So, the first piece of our music theory system: there are 12 tones [for teachers: "same number as months in a year" aids as a statement], and they lie ½ step apart.
One possible relationship between colors & music tones: