The word chromatic in music means 2 or more consecutive notes that are a half step apart from one another. A chromatic scale contains all 12 possible pitches before arriving back at the starting note name an octave higher.

Here are the notes in a C chromatic scale. You will see that there are only 12 different pitches before coming back to C. There are 12 different pitches, but you also see that the 2nd note in the scale is a C or a D. That is because C and D are just different ways to spell the same pitch. What you will call that pitch really depends on the situation.

C chromatic scale

C	C/D	D	D/E	E	F	F/G	G	G/A	A	A/B	B	C
1	2	3	4	5	6	7	8	9	10	11	12	1

Often sharps are used when ascending in the scale, and flats are used when descending.

When it comes to playing chromatic scales on the guitar, you are not necessarily starting and stopping on the "root" of the scale. In fact, you should not really think in terms of there being a root for this scale. Any note could be considered the root, and you are not really going to hear all of the notes in relationship to any one note. Playing chromatic scales is really just an exercise in understanding how the notes are arranged on the neck of the guitar. Understanding where the next note higher or lower is, even when switching strings. They are also excellence technique builders.

Page 2, Chromatic scale forms